Besides getting a supportive chair, a table set-up where your arms are at a 90degree angle, maybe tipping the machine with door stops etc (I do this on my lightweight machine, but doesn't work with the nicer machine with the table extension), you might also want to think about your lighting. I found that adding an Ott light over my sewing area really helped me see well enough so that I could relax and sit back in the chair more instead of hunching over the sewing. But even then, I sometimes just need to remind myself to sit up, shoulders back!
My "decadent" addition to my sewing space is one of those vibrating chair mats that my daughter gave me years ago for Christmas sit in the swivel rocker I have in the room--sometimes I take a break there!