Well bakhurts, I blew a disc in my back a number of years ago, and that was one of my many issues of continuing on my road bike. A good road bike can be relatively comfortable for a lot of people, however, if you want the most in comfort try a recumbent. This spring I switched to a recumbent, and it made cycling new and pain free again. Chillidog also rides a 'bent (actually two) and is a well rounded cyclist. Be prepared for some sticker shock though. Recumbents are somewhat expensive, but in my estimation, worth every penny.
'bent Brian
'bent Brian