First, fix what is making your body hurt. Presumably the problems are with your back or hands or both (and if not both, the other will come along soon enough).

First, fix what is making your body hurt. Presumably the problems are with your back or hands or both (and if not both, the other will come along soon enough). For your back, the solution is pretty well documented: chair that fits you, displays at eye level, keyboard at elbow level. For your hands, the solutions may be more personal, but likely involve (a) keeping your wrists straight and (b) kinesthetic feedback on your fingers.