I would wrap the handle with hemp string or jute, that will build it up to fit your hand. backing doesn't have to be sinew, I've backed with denim, silk, grocery bag paper, canvas, hemp cord, birch bark, ect. wouldn't hurt to have some extra insurance on your first few bows until you learn tillering and wood choice.
just take your time. If your design and tiller are good you shouldn't have alot of hand shock.
VB