Although I am not experiencing this matter, here are a few things I do know on the subject. Aerobics is the best exercise for the back, Taebo Live is a great one. Also, make sure you are resting at night on your side and not your back or stomach. You mentioned stretching, good continue doing that.
Sitting on a stool or bench
Sit up straight and maintain your lumbar curve to avoid the stress that leads to back pain. An easy way to do this is to make sure you are sitting on your "sit bones" (ischial tuberosites). You can feel these bones in your bottom when you tilt your pelvis back and forth while sitting. You can maintain proper posture without back support if you keep your weight over your sit bones, your back erect, and your chest out. This may feel awkward at first because it involves postural muscles that you're unaccustomed to using. But within a week or so, good posture will become a new habit.