6. The cotton batting should be fairly thin - 1.5 inches is about right.
I love sleeping on a futon, but what we have here is not the futon that most Japanese use for sleeping.
The bed has two parts, a 3.5 inch trifolding base of high density foam, and a 1.5 inch cotton batting pad that is laid on top of the foam pad to distribute your weight.
Part of the process of care involves placing the cotton pad on a rack daily to air out and beating it like you might do with a rug to fluff it and remove detritus.
Removable covers (in addition to sheets) for the cotton pad are usually sold separately.
Since airing and beating the 4-6 inch cotton batting mattresses used here is next to impossible I will not own one. I tried it once but it soon compacted to the firmness of marble, and acquired a musty moldy smell that made it seem filthy in comparison to what we are accustomed to.
I'd obviously recommend something else. A sofa and an inflatable air bed might be a good combination. The new airbeds are very comfortable and with a corded electric pump they are easy to inflate/deflate.