Wow. Lots of opinions here and many options. Here is my experience and thoughts.
First I totally agree with Inner Athlete about lengthening the Psoas. A tight Psoas can cause problems in the hips and affect the back. I have 2 herniated discs L4-5 L5-S1 with severe sciatica down my right leg. Driving and sleeping were extremely difficult and painful. My Doctor believes in non - invasive tx which is good. I did get a cortisone shot for the sciatica and began Physical therapy. As a yoga teacher I was quite familiar with many of the exercises they prescribed. I also learned much and brought that back to the classroom. Currently, through yoga and being mindful of my body my pain is almost gone. Sciatica is gone. I do feel like a new person.
Many areas of the body affect the spine. If you have tight hamstrings it will pull your pelvis and thus affect your back. A tight psoas will also pull the pelvis affecting the spine. Weak abs will also not provide the stability the spine needs. Yoga is perfect for back problems as it, if practiced correctly, will help balance out the musculature.
There are several yoga moves that are contraindicated for herniated discs such as twists and forward bends. If you have the guidance of a experienced yoga teacher you can perform these with modifications. Example: Most people come into a twist having the pelvic floor pressing firmly into the mat and then use their hand to get them farther into the twist. This can be a recipe for disaster for those with back problems. You must allow the pelvis to move with your spine as you twist and not use your hand as a torque. Another example are forward bends. People with back issues tend to round the back to try to get their hand to reach the floor. Hamstrings are usually tight, so they also bend their knees. This does not lengthen the hamstrings. They are stuck in an isometric contraction and do not lengthen. The back rounds before 90 degrees adding stress to the spine. My students use block to rest the hand in uttanasana while their legs are straight. (not locked) We work over and over in 1/2 forward bends (airplane) learning to keep the back straight until they get below 90 degrees. Then they can round.
Another often overlooked muscle group is the Multifidus. It runs the length of the spine and is very deep. Strengthening these will greatly add stability to the spine. There are a few sequences I do in class that works the multifidus and transverse abdominus and have been very effective for me personally and for my students. If you are interested, let me know and I can explain them.
As for sciatica, I use golf balls and roll over them in three different areas on the piriformis. Ouch! But is gets better. Learned this in PT and has been very helpful followed with either pigeon or reclined pigeon.
Extension of spine rather then flexion too. Bhujangasana, sphinx, bridge, locust and camel are a few that help. A bolster used for passive back bends while seated is awesome and feels great.
Gosh, I’m rambling now. Hope any or all of this helps someone!
Shanti!