I found the important thing was to keep it dry and well-aired. If you lay the futon directly on the floor, even wooden and/or carpeted, the heat from your body will cause condensation, and if you don’t let the futon air out by rolling it up, it will go mouldy. In Japan, futons are laid on tatami mats, which I imagine would cause the least condensation, and rolled up every day as a matter of course. I found it increasingly annoying having to deal with the futon every morning, especially in the winter when there was more condensation and it was harder to keep the futon completely dry. I like a firm mattress, but no more futons for lazy me.