I second Seamsright! Great quality, and the small is short along both the backs and the sides. I had one for my 14hh Arab his first year under saddle. We've since gone to a medium as he's grown, and has a different saddle now.
Agree with the Seamsright pads. I just ordered 4 custom felt pads which are terrific. They were great to deal with, just call and you can find out what measurements are needed and go from there. Great customer service and extremely fast shipping. I think I had all 4 custom pads within a week!
"Every little girl wants a pony so why should big girls be any different???"