Other forms: futons
A futon is a flexible mattress on a frame: it can either be folded up to use as seating or unfolded to use as a bed. When your cousins come to stay, they might sleep on a futon in the living room.
In the U.S., the word futon generally refers to the combination of a mattress and a light frame; in Japan, a futon is simply the mattress itself, usually stuffed with cotton and laid out on the floor for sleeping. If you visit a traditional Japanese home, you might sleep on a futon with a tatami mat beneath it and a duvet, or kakebuton, covering you.