Finding the right saddle is like finding the right bathing suit...there's no industry standard that everyone agrees on, so all the saddles come out different from different manufacturers (and some are better made than others, etc).
The Arab tree sounds like a good idea. Arab trees are usually shorter than standard trees, too. They also take into consideration the higher withers.
I tell everyone to go get a Flexicurve. It's a bendable, shapable measuring tape. They cost about $8-$10. You shape it to the contours of your horse's body in those hart-to-fit places like at the withers. Then you can just lift it off the horse and use it as a stencil for a withers tracing of your horse. You can use it to determine what kind of bars, what kind of flare, what kind of twist, and what size gullet you need without having to spend loads of money actually buying saddles only to find out they don't fit...and withers tracings are easily scanned into your computer for emailing, should you find a saddle online you might like (even on Ebay
!). It's really simple to do. (instead of a flexicurve you can always use a coat hanger or some wire from the hardware store, but the flexicurve actually has a measuring tape on one side and is quite pliable...coat hangers not so much. Lol)
Here's a link to a step-by-step on how to do a withers tracing. http://www.saddlersrow.com/file.asp?...pdf&C=articles