Years ago when my dad lived in the old house, my brother shared a room and we had a bunk bed and the bottom bunk was a futon. That was my bed. It was uncomfortable =/ The mattress is very thin and after awhile I could roll on it and count how many bars were underneathe it.
The sofa sleepers are nice. I sleep on one of them at my dad's current house if he's there, if he's not I steal his bed. It serves the same purpose- bed and couch. I think the bed is more comfortable and the couch looks more couch like than a futon
Someone mentioned a day bed. I had one. I never had a problem with it. I got rid of it when I got a twin a bed and had it move extended out from a the wall to the middle of my room (can't do that with a day bed). Now I have a full size bed and I bought a book case headboard for it. This is my favorite bed so far. When I first got the full size matress, it sat on my floor without a frame. That worked good to. Now I lose stuff under my bed -_-
Jam it back in, in the dark.