I'm 15 and I slept on the floor for a year. Here's why

When I was in my later teens and early 20's (my poor student days), I mainly slept on the floor in much the same way. My first proper bed post-school and gainfully employed gave me incredible back pains until I eventually got used to it.

Maybe it's why I sleep so well when camping. I still don't really see myself returning to those days, even though I'm sure it wouldn't be all that much of an issue.

The raised-bed-but-not-mattress, which I think you're picturing, definitely exists in the form of bamboo beds/'mattresses', which are just raised platforms of woven bamboo with a little give. They work well in places where a mattress would be quickly destroyed by humidity, but where air conditioning is uncommon (I've seen them in southern China).

Sleeping on a hard surface may cause issues with your back muscles, like knots, so I'd recommend researching this before trying it.

Back muscle includes fascia (overlapping layers) that can develop adhesions.

I did that for most of my 20’s as I did not have the space or money for a proper bed, and my back never hurt. In fact I remember staying in a hotel room for a night when I was about 25 and I woke up in the middle of the night with my back in terrible pain. Slept the rest of the night on the hotel room floor, and I felt a lot better.