I have been a physical therapist for 35 years and a quilter for one year. I know what you mean about back pain. It's not fun quilting when you're in pain.
A good chair is very important, as is the correct height of the chair. I use an office chair so that I can adjust the height of the seat of the chair.
Your back must be fully supported against the chair back. Sitting with your back unsupported by the chair back, means that your muscles have to hold your body up. This leads to over worked muscles, spasm and pain.
You should have your chair close enough to your sewing machine that you can sew with your elbows by your side and your whole back against your chair back.
Your sewing surface should be at elbow height. To achieve this, I raised my chair seat up, but this left my feet dangling. ( I'm only 5" 3" tall) So I placed a box that was 5" tall on the floor under my table and placed my foot pedal on it. One could also get their husband to make them a wooden stool that is about 20" X 15" and what ever height you need to sit correctly.
Works great. And best of all, no more back and neck pain.
I hope this of help.