Favorite sleep arrangement me and husband ever had was our so-called "hobo bed". A latex foam mattress topper, right on the floor. Done up with sheets like a bed, but nice and thin and low. We did that the first 3 years we were together. It was a ton of work though. With any flooring, you have to worry about moisture trapping, so I would move and flip it every week (I'm in Oregon, things are damp here over the winter). When you're on hard flooring, motes of dust work their way onto the edges of your sheets (and yes, I swept a ton). Then we lived in an old house with no protection against ants and spiders and centipedes at all, so that sucked. Eventually we gave up and went to a standard mattress. Much lower maintenance for me.
Mainly, I came to the conclusion that just one episode of mattress topper/floor rot would undo any savings, so it wasn't worth the risk. I know quite a few people that's happened to, actually. (College life, holla). And St. Vincent's here does or at least used to recycle inner spring mattresses and redo the upholstery. A whopping $90 for a like-new mattress. We used that for a few years, until a family member was moving and got rid of their guest room mattress. 10 years old, but barely ever used. Nice and firm. Score.
Anywhoo, for people who do legitimately like mattresses, they don't need to be spendy. For people who like floor sleeping, more power to ya, but be cognizant of the risks/challenges. Personally, it's just one more reason for me to love camping =) I get to be back in my hobo bed.