Mattresses make me feel like my body is being swallowed!
I like sleeping in "hard" surfaces. After weeks of sleeping on the living room floor over an exercise mat and a blanket, my husband finally listened to my pleas and got rid of our mattress.
Now it's in the basement against the wall, and it's used as a punching bag :-) My cat likes to sit on top and watch with big eyes as you punch the mattress. "Yeah, yeah, kill it! Kill it good!", she says.
I bought 3 foamy exercise mats, laid them side by side on the bed and cut them to fit snug with the bed (the bed has a slightly raised border to hold a mattress in place). Then on top of the mats I put 2 not so thick blankets. And then one of those thick foamy mattress covers. Those are excellent, by the way.
Total height of the mattress is about 1 inch and a half.
I put "hard" in quotes because I actually find this makeshift mattress very soft and comfortable, but other people freak out when they see my bed.
Because my husband likes a softer bed, I put an extra foamy exercise mat on his side.
It's been about 3 or 4 years that we've used this bed, and it still feels comfortable. I flip and fluff the bed maybe every 4-6 months (but you're supposed to do that with normal mattresses too).
For infants and toddlers, look at "Montessori floor bed" on google images (though some examples make me cringe).
I'm thinking of sewing a couple blankets together to form a twin-size mattress, then leaving one part open (like a pillow case) so I can put a hard exercise mat inside. With a hard exercise mat it won't bunch up.