by A mattress that felt supportive when you bought it can turn into a body-swallowing cloud over time. Foam breaks down, springs lose tension, and what was once a medium-firm feel drifts toward plush whether you wanted that or not. For back sleepers and stomach sleepers especially, too much give means too much spinal flexion, and that translates to morning stiffness, aches, and restless nights.
The good news: a softer-than-ideal mattress does not always mean an immediate replacement. Several fixes actually work, some for under $50. The key is diagnosing why the mattress feels soft before throwing a solution at it. This guide covers every proven method, ranks them honestly, and tells you when a fix stops making sense and a new mattress is the smarter call.
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Why Your Mattress Feels Too Soft
Before picking a fix, it helps to know what you are actually dealing with. There are four common culprits:
Normal foam compression. All foam compresses with use. A mattress slept on every night for three or four years will feel measurably softer than it did new. This is expected wear, and some of it is recoverable.
Wrong firmness from the start. Many people pick a mattress in a showroom after lying on it for two minutes. If the mattress felt borderline soft at purchase, it will only get softer.
Sagging or body impressions. This is different from normal compression. A mattress with a visible dip of 1.5 inches or more has structural damage. No topper or board will fix a mattress that has sagged past that threshold.
Warm room temperature softening foam. Memory foam is viscoelastic, it responds to heat. A bedroom consistently above 72°F will make a foam or hybrid mattress noticeably softer than the same mattress in a 65°F room.
Foundation issues. A broken box spring, widely-spaced slats, or a platform frame that flexes transfers softness upward. The mattress itself may be fine, but sleeping on a poor base makes it feel like it is not.
The 7 Methods: Ranked at a Glance
| Method | Estimated Cost | Effectiveness | Effort |
|---|---|---|---|
| Bunkie board | $50–$150 | High | Low |
| Firm mattress topper | $80–$250 | High | Low |
| Plywood under mattress | $20–$50 | High | Medium |
| Move to floor | Free | Medium | Low |
| Lower room temperature | Free | Low–Medium (foam only) | Low |
| Flip if double-sided | Free | High (if applicable) | Medium |
| Replace the mattress | $800–$2,500+ | Definitive | High |
Method 1: Add a Bunkie Board
A bunkie board is a 1–2 inch solid panel that slides between your mattress and its base. Bunkie boards are one of the fastest ways to firm up a mattress that is sinking into a slatted or worn platform frame. They work because they eliminate flex in the base. For foam and hybrid mattresses, this often produces an immediate and significant firmness increase.
Cost runs $50 to $150 depending on size. Setup takes ten minutes. The main limitation: if the mattress itself has a deep body impression, a bunkie board will not erase that dip. See also: Best Mattress for Back Pain.
Method 2: Use a Firm Mattress Topper
A firm latex or high-density polyfoam topper placed on top of the mattress adds a new comfort layer with more resistance than the worn surface beneath it. This is the most popular fix for mattresses that have lost their initial firmness but have no visible sagging.
Latex toppers in the 2–3 inch range are the gold standard here. High-ILD ratings (aim for 28 ILD or above) indicate a genuinely firm feel. Memory foam toppers are less ideal for a firmness fix because most are designed to add pressure relief. Budget $80 to $250 for a quality topper. Full guidance: Best Mattress Toppers.
Method 3: Slide Plywood Under the Mattress
A sheet of 3/4-inch plywood cut slightly smaller than your mattress and placed between the mattress and its base achieves the same result as a bunkie board at roughly half the price. Drill a grid of 1-inch holes across the board before installing it; solid wood blocks airflow and traps moisture. Plywood is most effective for innerspring and hybrid mattresses resting on old box springs. Costs $20 to $50.
Method 4: Move the Mattress to the Floor
Placing the mattress directly on the floor eliminates foundation flex entirely. This is a zero-cost test that can confirm whether your foundation is the problem. Sleep on it for a week. If the mattress feels significantly firmer on the floor, the frame or box spring is the issue. The downside: floors trap moisture, and most manufacturers void warranties if the mattress is used on the floor without a proper base, so keep this as a diagnostic measure.
Method 5: Lower the Room Temperature
This fix applies specifically to memory foam and hybrid mattresses with foam comfort layers. Memory foam softens as it absorbs heat and firms up as it cools. A bedroom kept above 72°F produces a noticeably softer feel than a room held at 65°F. Set the thermostat to 65–68°F before bed, run a ceiling fan, or use a cooling pad. It will not fix a structurally sagging mattress, but it can restore firmness to a foam mattress that has drifted soft from warm temperatures.
Method 6: Flip It (If the Mattress Is Flippable)
Most modern mattresses are one-sided by design. Do not flip a one-sided mattress. However, some older innerspring models and a few current double-sided designs are intentionally flippable. If yours qualifies, flipping exposes an unworn, firmer surface. Even non-flippable mattresses benefit from rotation head-to-foot every three to six months, which slows further softening.
Method 7: Replace the Mattress
All the methods above work on a mattress that has softened but still has its structural integrity. When the mattress has a body impression deeper than 1–1.5 inches, when coils are audibly creaking, or when it is more than 8–10 years old, fixes become diminishing returns. A sagging core will push through any topper within months.
This is also the case for sleepers who bought the wrong firmness to begin with. If you need genuine lumbar support, the right move is a mattress built to the firmness you actually need. See: Mattress Sagging Fix Guide and How Long Do Mattresses Last.
Which Firmness Level Is Right for Your Sleep Position?
Back sleepers generally do best on medium-firm to firm (6–7 out of 10). Stomach sleepers need the firmest surface, typically a 7–8; excessive give allows the hips to sink and hyperextend the lumbar spine. Side sleepers are the exception, requiring some give at the shoulder and hip. Heavier sleepers (over 230 lbs) compress foam faster and may need higher-density foam or a stronger coil system. Detailed comparisons: Firm vs. Medium Firm Mattress and Best Firm Mattresses.
When a Fix Works vs. When You Need a New Mattress
Use the fixes above when the mattress is under 6 years old with no impressions deeper than 1 inch, when the problem is the foundation, or when you bought a slightly-too-soft firmness. Consider replacing when body impressions are 1.5 inches or deeper, you wake with back pain that resolves within an hour of getting up, the mattress is 8–10 years old, or you have already tried a quality topper and still wake sore.
A luxury firm hybrid is the most versatile replacement for back and stomach sleepers. Hybrid construction provides the push-back that all-foam mattresses lose over time, and the coil layer is inherently more durable than foam alone.
Frequently Asked Questions
Can a mattress topper actually make a mattress firmer?
Yes, but only with the right material. A firm latex topper (ILD 28 or above) or high-density polyfoam topper adds a resistant surface layer. Soft or medium memory foam toppers will not help, they add pressure relief, not firmness.
Does putting plywood under a mattress work?
It works well for mattresses on old box springs or widely-spaced slats. A 3/4-inch plywood sheet creates a rigid base. Drill ventilation holes before installing to prevent moisture buildup. It will not fix structural sagging.
How does room temperature affect mattress firmness?
Memory foam softens as it absorbs heat and firms up in cooler conditions. A room kept at 65–68°F produces a noticeably firmer feel from a foam mattress compared to a 72°F room. It cannot overcome significant foam compression.
What is a bunkie board and is it better than plywood?
A bunkie board is a manufactured 1–2 inch panel designed as a mattress base. It functions the same way as plywood but is purpose-built and fabric-wrapped. Both work equally well; a bunkie board is more convenient, plywood is cheaper.
Should I flip my mattress to make it firmer?
Only if your mattress is explicitly double-sided. Flipping a one-sided mattress places the firm support core on top, which is uncomfortable and can damage the materials. Rotation head-to-foot every three to six months is safe for all mattresses.
How do I know if my mattress is too soft or just broken down?
Look for a visible body impression when the mattress is empty. A dip of 1 inch or less is normal wear; 1.5 inches or more indicates structural breakdown. Coil noise, an uneven surface, or consistent morning back pain also point to breakdown.
What firmness level should a back sleeper choose?
Medium-firm to firm, roughly a 6 to 7 on a 10-point scale. Heavier back sleepers (230 lbs and above) often need a 7 or 8 to prevent the hips from sinking below the shoulders.