Mostly I sleep on a bed because it is the social norm.
Sleeping on the floor or on the ground takes some getting used to but for me, I feel better when I do. I don't have back problems, it's just nicer.
I bought the firmest mattress I could, but it was also very cheap. I've had it for only a few months and already I can feel the springs through the fabric of the mattress. Time to get some padding. Or go back to sleeping on the floor.
In my current room there's not enough floor to sleep on with a full sized bed in here. When I get my house I'll have 3 bedrooms and I might just turn this bed into a guest bed.