The Best Daybed Mattresses

Eight inches on top, and why that number

Eight inches is the figure that lands correctly against a typical daybed side rail: deep enough for a real support layer, shallow enough that the sides still read as sides rather than as a lip the mattress is spilling over.

Read the twin capacity. 250 pounds against 500 for every larger size is a real difference, and twin is exactly the size a daybed takes. If the sleeper is heavier than that, a coil-based hybrid is the sounder choice.

A four-inch high-density base is what stops the mattress dishing where the weight is, and it is the reason eight inches lasts where six does not under regular use.

Six inches below, because the tray is shallow

A trundle is a tray on castors and it has to slide back under the daybed with a mattress in it. Six inches or less is the hard limit, and on some frames it is less — a DHP Astoria trundle frame is 3.5 inches tall in itself, which tells you how little vertical room there is once it is under the daybed.

A six-inch innerspring is the usual answer: heavy-gauge steel coils under a quilted cover with a foam comfort layer, shipped compressed, and firm. It is a guest-frequency surface, which matches the 225-to-250-pound trundle capacities on most frames anyway.

Measure your own frame before ordering. Pull the trundle out, measure from the deck to the underside of the daybed rail, and subtract half an inch for bedding.

When a tri-fold makes more sense than either

If the daybed has no trundle and you only occasionally need a second bed, a tri-fold mattress in a cupboard beats a trundle you never use. A Milliard six-inch tri-fold is 75 by 31 inches flat and folds to a folded size Milliard does not publish — it stands in a wardrobe.

Two honest caveats. It is cot width at 31 inches, which is seven inches narrower than a twin. And the two fold lines are findable through six inches of foam if you sleep on your side.

For a guest who stays twice a year, that is a good trade and it costs you no permanent floor. More formats that behave this way are in Japanese floor futons.

The fit details that decide how it looks

Against the rails. A mattress noticeably deeper than the side rails slides, because nothing is containing it. A mattress much shallower makes the daybed a box. Measure the inside height of the rail and match it within an inch or so.

Length. Daybed frames are built for a 75-inch twin. A twin XL at 80 inches will not fit, and the overhang is not fixable.

Sheets. A daybed takes ordinary twin sheets, which — after the sofa-bed sizing on the rest of this site — is a relief worth mentioning. Use a pocket depth matched to the mattress; deep-pocket sheets on an eight-inch mattress bunch.

Bedding storage. If the trundle is not in daily use, the trundle is the bedding store. If there is no trundle, a flat box under the frame is better than anything across the room.

Comfort fixes that do not involve replacing the mattress are in how to make a daybed more comfortable.

If you are still working out which size your frame takes rather than which mattress to put on it — twin against full against a pop-up trundle pair, plus the published depth limits frame by frame — start at what size mattress for a daybed.

One thing the mattress cannot fix: a daybed ships with no back cushions, so the sheets are the easy half of the bedding decision and the wedge against the back rail is the half that decides whether anyone sits on it. Both are covered in the best daybed bedding.