Convertible sofa beds aren't usually very comfortable, in fact, they generally have a reputation for being lumpy or slanted or for having a metal bar that seems to run right across the middle of the bed. Although, more recently, higher-end convertible couch beds may have mattresses that are more comfortable to sleep on, most people are still using ones that do more to keep you awake than help you sleep. Fortunately, there are some quick fixes you can do to make the convertible sofa bed more comfortable for yourself or a guest.
Purchase a mattress topper for the convertible sofa bed that is thick or made from a material designed to mask underlying faults in a mattress. Foam or down/synthetic feather mattress toppers are good for convertible sofa beds because they are not only comfortable in and of themselves, they will provide added padding to the mattress beneath. A down mattress topper can be very warm and may not be ideal for high temperature climates. Down can also be an allergen, so purchasing a synthetic feather alternative may be a safer bet. Foam mattress toppers are thinner, but they are also less expensive and they will provide a softening effect to the lumps and bars of a convertible sofa bed.
Use a heavy blanket, such as an unzipped sleeping bag or a thick comforter in place of a mattress topper. Although the effect will not be quite as masking, a heavy blanket or comforter will do in a pinch. You can use more than one to help thicken the distance between you or your guest and the convertible sofa bed mattress.
Grab some extra pillows---even the couch's pillows will work---to close the gap between the back of the sofa itself and the sofa bed. When sleeping on a convertible sofa bed, your regular pillows can shift and slip down between the back of the couch and the bed during the night, which doesn't happen on a regular bed because of a headboard or the wall. Stuffing the gap with couch pillows will prevent you from waking up in the middle of the night to fish your pillows out.
Find some small books or a small stack of newspapers or some cardboard you can fold to place under the legs of the convertible sofa bed to level it out. Sofa beds often seem to slant downward, toward the back of the couch, which can be very distracting when trying to sleep. You can use thin books, newspapers or folded cardboard to put under the couch itself or under the legs of the bed portion to create a more level plane to sleep on.