is first of all both futon mattress and futon frame. Since the frame can be made from either hard or soft wood. Examples are Oak or Pine and there's usually considerable choice.
In addition 2 seat futon sofabed frames often have arms as an optional extra, some clip on and others fixed.
Futon mattresses suitable for this double or king size usually have at least 6 layers of filling and a 100% cotton drill mattress cover. Colours are often part of the package choice. A futon mattress of this type will be buttoned to keep the filling in place.