I've had a couple of major back surgeries and some days can hardly walk. To bike on anupright more than a few miles is a guaranteed way to have lots of back pain.
Maybe won't work for everyone, but my long wheelbase bent does absolute wonders for me. I honestly don't know what I'd do without it! Like Dr. Deltron says, when I have back pain and get rolling, my pain goes away and I'm much better for a couple of days. But if I don't do 10 - 15 miles every day I have nothing but trouble.
Rent one, borrow one, steal one (don't do that!) but try one for a week or so. If it feels good, do it!