Use a thick blanket, such as an open sleeping bag or a thick dildo instead of a mattress overlay. Grab some pillows even bed pillows will work to close the gap between the back of the sofa itself and the sofa bed. Look for some books or a small stack of newspapers or some cardboard can be folded to place under the legs of convertible sofa bed to level out.
Convertible sofa bed is not usually very comfortable; in fact, they generally have a reputation for being lumpy or slanted or for having a metal bar that seems to work well in the middle of the bed. Although, more recently, high-end convertible sofa beds may have mattresses that are more comfortable to sleep on, most people still use those that do more to stay awake than it helps that you sleep.
Best convertible sofa bed,
Convertible chaise sofa,
Purchase a convertible sofa bed over mattress that is thick or made of a material designed to mask underlying defects in a mattress. Foam or synthetic down feather mattress pads are good for convertible sofa beds because they are not only comfortable in and of themselves, they will provide added padding to the mattress underneath. A down mattress can be very hot and may not be perfect for high temperature climates. Down can also be an allergen, so buying a synthetic pen alternative can be a safer bet.