I've slept on floor many many times - however, I'm usually on my back and then start snoring. Not good for my bed mate :)

Was very close to getting a Shikibuton. On man this one really had me drooling: http://soaringheart.com/products/organic-cotton-wool-shikibu...

even a cheap exercise mat works well, I just can't stand sleeping on plastic though....

Ended up with a traditional mattress from the Original guys because we already had a matching bedroom set and my mate didn't want to drop $$ on a new setup...