If you imagine a thin large Japanese mattress when you hear about queen size futon, you are right…and wrong. Really, time ago futons were soft mattresses used as beds directly on the floor. The tradition has come to us from Japan, but in the process of trying various designs it was “modified”.
Today queen size futons are solid bases which can fold and unfold and a mattress over them. You do not sleep on the floor any more, but you use the same Japanese bedding, so compact and convenient. As queen size referres to the dimensions equal 80 inches x 60 inches large queen size futon resembles a queen bed when it is opened and ready to welcome its owner to sleep. These units are cheap.
If you have a base at home (some masters do these bases themselves), you can pick any futon to match it. The size is important only, not design. If you want it, you can use futon mattress without a base: just for fun (some people like sleeping on the floor) or as an additional bed for guests if your buddy comes to you unexpectedly and stays for a night or two.
Modern futons of queen size can excellent replace sofas and even couches in contemporary apartments and in studios. Some large futons are designed to be used with no base: they transform into a chair or an armchair, an ottoman, and additional mattress. To make the lifespan of these mattresses longer, you should buy or sew a cover for it. When it get stains, just unzip the cover and wash it in a washing machine.