I always had a futon so I immediately switched to that. I also bought a cheap hammock and built some hammock stands to use it indoors.
I didn't have any problems adjusting to the futon; that's what I sleep on most of the time today. I'm also pretty sure I'd have no problems with a japanese style roll up beds either (it's basically like a futon anyway).
Hammocking, though, took a bit longer. I really wanted to make it work too. To make a long story short, my initial hammock was too short and now I do have a hammock I can sleep soundly in (which I do every now and then).
I was also initially interested on trying to train myself to sleep on a flat floor... but, ummm, that did not go well and I've never returned to trying. Maybe...