I worked for years in a sewing factory. Each machine had a different function so different heights were necessary, however, for stitching as we do while quilting, typical height is between 26 to 29 inches. Sit with your back comfortably straight (don't over do it), your hips and knees at 90 degree angles. Next hold your elbows slightly above or below a 90 degree angle. where your wrists lay will give you a pretty good idea of height. If you DH builds with wooden legs, have him make it a little taller than what you think you need, that way you can sew on it for a few days and he can always shorten the legs easily.
If your shoulders hurt and you find yourself stooping over at the neck, it is too short. If your shoulders hurt because you are having to lift your hands hight (elbows at wrong angle) than it is too tall.
Also, a cheap chair from discount store that adjusts height would be great. Some days you need a little height, some days you may want to be a little lower.
Hope this helps sorry so long winded.