Would sleeping or laying on the floor really be better for your back?

I think a part of your question is missing.  Is sleeping
on the floor better than what?  Better than sleeping in a
bed?  I actually don't think so.  I do think, however, that generally speaking, a hard
mattress is better (in the long run) than a soft mattress or even a pillow top mattress.
 I realize many people swear by soft, cushy mattresses - but the fact is, they do not
keep the spine aligned.  Instead, the put a curve in the spine in the direction of the
heavy part of the body.  For example, if you lay on your back, rather than keeping your
spine straight (as if you were standing with good posture) there would be a natural bend
from the weight of your hips and bottom.  Over time this nightly stress on the spine can
result in muscle pain - or worse - disc issues.  The same is true for sleeping with the
wrong kind or size of pillow - over time it can result in prolonged neck tension and
pain.

As a result of something completely unrelated, my
husband ruptured a disc in his lower back - and had surgery.  Ever since then, he's
sworn by a firm mattress - and he would say that sleeping on the floor is certainly
better and more comfortable than sleeping on a soft
mattress.

A chiropractor would tell you that the health of
the entire body can be tracked back to the health of the spine - so anything you can do
(starting with good posture) to keep yours healthy and strong is one of the best things
you can do to protect term health.  Trust me when I say that your body might likely
never feel (or look) as good as it does right now.  :)