How to make a sofa bed more comfortable.

Three things work against a sofa bed. The first is the mattress. Because it has to fold into the sofa, it is thin: a sofa-bed sizing guide gives about 4.5 inches as the standard height, far thinner than a normal mattress.^[6] The second is the frame. The mattress rests on a folding metal mechanism, and on many sofa beds a support bar crosses under the mattress at about the height of your back. A thin mattress does not hide it. The third is wear. Springs, the fabric deck that holds the mattress and the foam itself all lose their shape over years of folding.

There is also the person sleeping on it. A sofa bed is usually a guest bed, and sleep in an unfamiliar place is lighter on the first night. In a 2016 brain-imaging study, people sleeping somewhere new for the first time had one side of the brain sleeping less deeply than the other, and unusual sounds picked up by the lighter-sleeping side woke them more often; by the next session the difference was gone.^[1] A guest on a sofa bed gets both problems at once: a new room and a thin mattress.

No study has tested sofa beds themselves. The mattress research that does exist points in a useful direction, covered below: firmer is not automatically better, and people moved from old beds to new ones reported better sleep.

The bar is a common complaint, and a topper alone often does not solve it, because a soft layer on top still bends over a hard bar underneath. The usual fix is to spread the bar out: lay a thin, rigid board, such as a sheet of plywood or a folding support board sized to the frame, across the mechanism under the mattress, or put a folded blanket over the bar. This is a practical fix, not a tested one. Check that the bed still folds; if the board stops it closing, take it out and store it with the bedding.

Sagging is different. If the middle dips because the springs or the deck have stretched, or the foam has broken down, padding on top follows the dip rather than fixing it. That is the point to replace the mattress. If the frame itself bends, rocks or will not sit level, a new mattress will not fix it either: the frame needs repair or replacing.

The research on beds does not support simply making a bed firmer. In a randomised trial of 313 adults with chronic low back pain, those given a medium-firm mattress had less pain in bed and less disability after 90 days than those given a firm one.^[2] A 2021 review of 39 studies reached the same conclusion: a medium-firm mattress promotes comfort, sleep quality and spinal alignment.^[4] For a sofa bed, the goal is an even, medium surface, not a harder one.

Once the support is even, a topper deals with the thin, hard feel. In practice, a 2- to 3-inch topper is the usual choice for a sofa bed. Thicker toppers add more cushioning, but they are harder to fold away and store. Whether a topper can stay on when the bed folds depends on the mechanism; thin ones, under about 2 inches, are the most likely to fit. Test it: if the bed will not close easily with the topper on, the topper comes off before you fold it.

Size matters more than on a normal bed. Sofa-bed mattresses are usually about 72 inches long,^[6] against 80 inches for a standard queen mattress. A standard queen topper will hang about 8 inches over the foot. Fold the extra under the mattress or buy a topper sized for a sleeper sofa, and use straps or a fitted cover so it does not slide off the narrow mattress in the night.

If the sofa bed is used every night rather than for occasional guests, the same fixes help, but the thin mattress is a compromise built into the design. The mattress research below is about beds people sleep on nightly, and it favours a new, medium-firm surface over an old, worn one.

Replace the mattress when it sags, when you can feel the springs or the bar through it even with a board underneath, or when the foam no longer springs back. The evidence that this helps comes from normal beds rather than sofa beds: in a study of 59 healthy adults with minor sleep-related pain, whose own beds averaged 9.5 years old, sleep quality improved and back discomfort fell over 28 nights after the beds were replaced with new medium-firm ones.^[3] The study had no comparison group, so it shows the change rather than proving the cause.

Sofa-bed mattresses are not standard sizes. One sizing guide lists sizes including queen at 60 by 72 inches or 58 by 72, a wider queen at 64 by 72, full at 54 by 72 or 52 by 72, three-quarter at 48 by 72, and twin at 38 by 72 or 35 by 72, with a standard height of 4.5 inches.^[6] The same guide warns that if your current mattress is thinner than 4 inches, a 4.5-inch replacement may stop the bed folding.^[6]

So measure before you order. Open the bed, take the mattress off, and measure the inside of the metal frame, width and length, rounding down to the nearest inch.^[6] Note the thickness of the old mattress. Check the seller's return policy before ordering a non-standard size, because a mattress cut to an odd size can be hard to return.

A sofa bed usually sits in a living room, which was not set up for sleep. The same three things that matter in a bedroom matter here: heat, light and noise. With normal bedding, research found sleep held steady across a wide range of room temperatures, but heat, especially humid heat, increased waking and cut deep and REM sleep.^[5] Keep the room from getting hot and use bedding that suits the season.

Noise matters more than usual on the first night. In the first-night study, the lighter-sleeping side of the brain responded more to unusual sounds, and those sounds caused more awakenings.^[1] Give a guest a sleep mask and earplugs, turn off or cover standby lights, and keep the hallway quiet. Give them a proper pillow too: a guest using a sofa cushion as a pillow may wake with a sore neck that has nothing to do with the mattress.