Some people have found yoga to be very helpful in relieving back pain (and pain in other areas of the body). I teach a restorative type yoga class that focuses on balance, flexibility, toning, and relaxation. One participant mentioned that she used to have to go to the chiropractor every week or two. Now she only goes about every 4-6 months. I've also had people to tell me that they can sing better (lots of practice with deep breathing in the class) and quite a few participants have had replacement surgeries and have come back as soon as they were released by their physician.
If you are looking for a yoga class, find out what types of styles are available. Some move rather quickly from pose to pose and add a cardiovascular component with less focus on form and toning. In some styles, they heat the room temperature VERY warm and may move into quite challenging levels.
If you've been through any type of physical therapy and find it hard to continue doing the exercises on a regular basis on your own, you may wish to find a yoga class that incorporates many of those exercises in the class. Many instructors encourage participants to mention any problem areas so that the instructor can particularly focus on those areas and provide modifications if needed.