Your best bet is to get a bunch of saddles and start trying them.
I would recommend trying a KN (Karl Niedersuss) if you can get your mitts on one. They are quite inexpensive - even new - because they are a very no-nonsense saddle. I got mine from Dressage Extensions in California - they shipped it up to me in a week and said to send it back if I didn't like it. They try to keep a lot in stock - but if you do want a short or long flap, or any other custom thing it will take longer because they do have to ship from the saddle maker in Austria.
A good saddle fitter will know what shapes and makes will fit your horse best and lessens the trial and error considerably.
Thanks Anabel! I do have a great fitter, she just doesn't happen to have anything that I like right now. I've gotten pretty educated to fit saddles to the point where I know when we've got a close fit, then I call my fitter in for her opinion and adjustments.
I decided to bite the bullet and take those two out on trial. I'll post fit pics next week when they come! The only thing I'm a little worried about is getting something while he's rehabbing. I won't be able to trot / canter in it while it's on trial. But, I'll be able to get the fitter out to take a look before I have to make a decision.