Ray (Latitude Adjustment) hit the nail on the head. If you’re contemplating back inflation, backplate is the way to go. The harness can be adjusted to whatever your size is. The only thing to consider is if you’re short in height, you may want to look into a short backplate. As far as positioning of your body on the surface, there’s no real difference between my first jacket BC and my current backplate setup. Plenty of times, I floated on my back wearing the backplate with a wing.
Many people are paranoid about the whole "What if you’re unconscious"? A) That’s what a good, competent, responsible buddy is for. B) Let’s give ourselves the best advantage with high quality equipment, competent training, sufficient practice and ample preparation/planning to minimize the risks.
One final point I’d like to make is an entire backplate package will be a little more pricy. But you can pick and choose which manufacturers you want to use.