I use a support that I found at Home Depot that's for supporting boards that you're running through a power saw. It has an adjustable angle on the table, slides up and down easily, and best of all, folds flat when I'm not using it. I think it was about $25.00.
If you're really cheap, get one the low end office chairs with a small backrest. You can flip it around and the subject lean their elbows on the back of the chair, and you can slide the back rest up and down.
If you do a lot of studio work, Photogenic is nice... David Buzzard