What I did was this, and my back aches stopped. I was using a straight backed chair...so I switched to a computer chair, and raised it all the way up..I did this to keep my wire fox terriers from chewing on the handle..I was afraid they would 'drop me'. So, I noticed my back stopped hurting...tension left in the back also.
I use a 6 foot folding table for my sewing machine, and it all seems to work great so far.