Wikipedia futon:

A complete futon set consists of a mattress (敷き布団, shikibuton, lit. "spreading futon") and a duvet (掛け布団, kakebuton, lit. "covering futon")

However, Western-style futons, which typically resemble low, wooden sofa beds, differ considerably from their Japanese counterparts.[1][16] They often have the dimensions of standard western mattresses, and are too thick to fold double and stow easily in a cupboard. They are often set up and stored on a slatted frame,[13] which avoids having to move them to air regularly, especially in the dry indoor air of a centrally-heated house[17] (most Japanese homes were not traditionally centrally-heated[18]).

"Western-style futons" don't really sound like futons at all tbqh.