It all depends on your horse's back. Some horses are ok with just the AP pad, but it makes ME feel better to have at least a half pad too! :) I always use a sheepskin half pad (Fleeceworks, Mattes, etc) because it offers a little more protection and comfort for their back. If he needs anything more I'd use a gel pad or something that can absorb more shock. I always use the AP pad directly on the horse, and then the gel/half pad between the AP pad and the saddle. Quilted or non quilted doesn't make too much of a difference. If you use something thinner (like a baby pad) I'd definitely put some more cushioning in there.