I injured my back several years ago, and workers comp sent me to a therapist and called it "back school". There I learned when standing for long periods of time ( I do it now for even short ones) relax knee, do not keep it rigid, and place other foot up on something at least 2 inches high. it takes the pressure off your back. Alternate legs if standing a long time. For sitting, the knees should be higher than the hips. So I put something on floor under sewing table to put mu feet up on. Every so often, the foot petal falls off, but putting it back is easier than back discomfort.
I was at Verizon the other day and they have a bar for the standing workers to use at the work stations. I thought that was neat.
I hope this helps you enjoy our wonderful craft, I would go stir crazy if I couldn't sew!!!!!