by A split king "mattress" is technically two Twin XL mattresses (38" x 80" each) placed side by side on a King-size frame or dual adjustable bases. Buying for a split king setup means shopping for Twin XL mattresses — one per person — that are adjustable base compatible.
Sleep Lab Pick · Current Sale
Amerisleep's Current Sale: $500 off every mattress. The AS3 — plant-based Bio-Pur® foam, sleeps cooler than memory foam, 100-night trial, 20-year warranty.
Shop the $500-off sale →Here's what to look for and the best Twin XL picks for split king setups in 2026.
Split King Mattress Requirements
Not every mattress works in a split king setup. The key requirements:
- Twin XL size (38" x 80"): Not Twin (38x75). You need the extra length.
- Adjustable base compatible: If using with adjustable bases (the main reason for split king), the mattress must flex without cracking. Memory foam and latex work. Traditional innerspring doesn't.
- Minimal motion transfer: Since you're already getting zero motion transfer from the physical separation, the mattress material matters less here — but a quieter mattress (foam, latex) still contributes to undisturbed sleep.
Best Split King Mattresses in 2026
1. Amerisleep AS3 Twin XL — Best Overall for Split King
The AS3 is our top pick for split king because it checks every box: adjustable base compatible, medium feel that suits most sleepers, CertiPUR-US certified, and backed by a 20-year warranty. Both partners can order the same mattress (if they share firmness preferences) or different models (AS2 firm vs. AS5 plush) for truly personalized sleep.
- Available in Twin XL — order two for split king
- Bio-Pur plant-based foam — adjustable base compatible
- Medium (5/10) — most versatile firmness
- 100-night trial, 20-year warranty
- Can mix and match AS models for different firmnesses per side
Order two Twin XL AS3 mattresses for a split king setup. Medium feel (5/10), Bio-Pur foam, adjustable base compatible. 100-night trial, 20-year warranty.
View Amerisleep AS3 Twin XL →
2. Puffy Lux Twin XL — Best Hybrid for Split King
The Puffy Lux is a pocketed coil hybrid with a climate-adaptive cover — one of the few hybrid mattresses that is fully adjustable-base-compatible and available in Twin XL. If one or both partners prefer a hybrid feel (bouncier, better edge support, cooler sleeping), the Puffy Lux is the best Twin XL hybrid available.
- Available in Twin XL
- Pocketed coils — adjustable base compatible
- Climate-adaptive cover for temperature regulation
- 365-night trial, lifetime warranty
Order two Twin XL Puffy Lux mattresses. Climate-adaptive cover, pocketed coil hybrid, adjustable base compatible. 365-night trial, lifetime warranty.
View Puffy Twin XL Mattresses →
Mixing Firmnesses in a Split King
Frequently asked questions about this size
Our default pick at this size
Saatva Classic — Split King $3,199 (was $3,599, −$400)
The Saatva Classic is the most-ordered luxury hybrid on the US market and ships in every standard size. Zoned lumbar support, 365-night home trial, lifetime warranty, free white-glove delivery + old-mattress removal included.
What are the standard mattress size dimensions?
Twin: 38"×75" | Twin XL: 38"×80" | Full: 54"×75" | Queen: 60"×80" | King: 76"×80" | Cal King: 72"×84". Oversized specialty sizes (Alaskan, Wyoming, Texas) run from 80"×98" up to 108"×108".
How do I choose the right mattress size?
Three-factor rule: (1) tallest sleeper + 6" = minimum length needed, (2) 30"/person minimum width (more if you bed-share with kids/pets), (3) bedroom layout needs 2' walking clearance minimum on one side. Size up when any of these is borderline.
Does Saatva make every mattress size?
Yes — the Saatva Classic comes in Twin, Twin XL, Full, Queen, King, Cal King, and Split King. All sizes ship with free white-glove delivery.
One of the biggest advantages of a split king setup is the ability to buy different firmnesses for each side. Common combinations:
| Partner 1 | Partner 2 | Recommended |
|---|---|---|
| Side sleeper, prefers soft | Back sleeper, prefers firm | AS5 Plush + AS2 Firm (Amerisleep) |
| Hot sleeper | Normal sleeper | Puffy Lux (cooling) + Amerisleep AS3 |
| Organic preference | Foam preference | PlushBeds Twin XL + Amerisleep AS3 |
Frequently Asked Questions
What mattress size do I need for a split king?
Two Twin XL mattresses (38x80 inches each). Not Twin (38x75) — you need the 80" length. Together they create the same 76x80" footprint as a standard King.
Can you use different mattresses in a split king?
Yes — this is one of the main reasons couples choose split king. Each partner can choose a completely different mattress (different brand, firmness, material) as long as both are Twin XL and adjustable-base-compatible.
Does a split king mattress have a gap in the middle?
There is a seam between the two Twin XLs, typically under 1 inch when pressed together. Many users add a mattress gap filler pad across the seam. Noticeable primarily when rolling from one side to the center.
How much more does a split king cost than a regular King?
Mattress cost: 20-40% more than a standard King (two Twin XL vs. one). Larger cost difference: dual adjustable bases add $3,000-5,000 compared to a platform frame setup.