Not sure if this would help, but in my searching to find a western saddle for Mr. Uber Short Back man, I've seen quite a few saddles listed with Haffie trees.
Some synthetic and some not.
I haven't checked into them and don't know how different they are, but I know that some gaited horses do much better in a gaited tree, while others don't.
Maybe if you find out what makes them different (I'm guessing its not just a ploy with Haffies being quite differently made) then you could apply that info towards a regular western saddle.
If you have ever considered an aussie saddle, just calling Down Under Web could get you loads of info as their customer service is great and they will answer just about any kind of question you can think of in regards to fit... no matter how many questions you may have.
(uh huh... ask me how I know)
And much of the info can translate over to western. Thay (as well as others) have some good YT videos out there on taking saddle fit measurements, which isn't hard to do at all.
Digby thinks it actually tickles a little bit, but as long as he gets a belly rub along the way... he will stand for any kind of measurements known to man.