Follow-Up:
I've been sleeping in a soft-sided waterbed since 1998. I am getting ready to go shopping for a medium-firm mattress after having just seen a chiropractor for an achy lower back. A waterbed does NOT provide proper support for your back or entire body, for that matter. As a matter of fact, I believe sleeping in a waterbed all these years might have contributed not only to my lower back discomfort, but to hip pain on my left side.