I also have back issues and I have found that sewing on my cutting table (which is propped up with bed risers) using a bar stool helps to keep me from "hunching over" which my therapist says is the worst thing ever for your back. (I do sew on the regular sewing spot if it is just a couple of minutes or so.)
I love my TENS. I get neck/shoulder pain also (which is caused by my bad spine).