Years ago I used this one and it did seem to help:
http://search.nancysnotions.com/?q=b...h=&sp_cs=UTF-8
I used to have back problems until my doctor sent me to a clinic that specializes in exercises for back and neck pain. They checked out my MRI first to make sure it was safe, then put me through a series of strengthening exercises on their workout machines that were able to isolate specific muscles. I went twice a week for something like 10 weeks. Have not had any back problems since then. However, nowadays I never sit and sew for longer than an hour at a time (usually less) without getting up and doing other activities in-between. Also, I continue to use a Roman chair for back exercises.