We've been looking at a new bed for DS with a double bed on the bottom and a twin bunk on top. Does anyone have any experience with having just a mattress, not box springs? I'm particularly concerned about the bottom double, because it maybe wouldn't matter so much for a child, but when relatives visit, they usually get my son's room, and I'd like it to be comfortable. The salesman is telling me it won't matter, but I don't know if I believe him. He says we could opt not to get the drawers that are underneath and lower the rails to put a box springs in if we wanted.