Step 52: Bedding
I measured the distance from inside wall to inside wall, and then cut the mattress about a inch wider than that. I wanted it snug in place. It worked out really well.
Two inches might be a little thin for some. When I sit on it, I can feel the floor, but when I stretch out I don't. If it becomes a problem, we can add a second layer of closed cell foam. My wife is going to sew up some special sized sheets and whatnot.