I can't find a free link to it, but an episode of Penn &Teller's Bullsh*t addressed yoga and various other "new age" shite.
If you have genuine spinal issues, doing any kind of twisting or contorting could cause serious injury and problems.
Generally speaking Yoga is more of a mental/meditation process than a physical one. Yes, there are physical aspects of Yoga, but in that regard it is not any different than the normal stretching any athlete would perform prior to competing or working out.
I would take it as an axiom, that the vast majority of Yoga instructors have little or no knowledge of actual physical ailments and how any given Yoga pose may be beneficial or dangerous for any one of those ailments.
So the fundamental question is what is the cause of your back issue.
If it is simply muscle related, then there are a host of stretching and isometric exercises you can do to address that. Any capable physical therapist can walk you through that in a few sessions and then you could do it on your own.
If you have health insurance, you likely can get a few sessions paid for, if you can get a script from a doctor that you need it.
If it's not muscle related, but structural, then trying to do flexibility exercises is potentially very risky.
If you don't know what is the cause, then I would strongly recommend you go through the goat f*ck that is such a diagnosis process to make sure you know what's wrong and so can devise an appropriate treatment option.
Oh and for the record, I am intimately familiar with just how painful that goat f*ck can be.
I have a neurological condition that took 6+ years to properly diagnose.
