Yes there are all types of yoga from pseudo-religious through to extremely practical. I've done some holds in some classes that would've been amazing for strength (they left me sweating).

As the other poster said though I prefer pilates, and in particular pilates reformer (with the bed) seems very good for back pain since in a lot of exercises you can support your back to varying degrees depending what you need at the time. The springs means it's not technically just body weight but it seems about right for me, at this time.

I'm definitely a short hamstring sufferer who could stretch more and need to work that in.