Be more definative. What is
It sounds like you have tried some that were too wide and sitting down on his withers.
We keep about 25 western saddles for our operatoin so we can fit various body types. The saddle the fits the most is a flex panel by Timberline. Not saying all flex panels fit most horses, but with some smart design criteria, this one fits most.
If you want some help from really knowledgable people, call the folks at Timberline. I hauled my horse from South Carolina to Missouri and spent a day with the staff. You may not want to do that, but their master saddle maker is a pretty sharp dude. I was impressed when we talked on the phone about a second saddle. Earl is very insightful. So many other places you get a sales rep that wants to sell, not help. http://www.timberlinesaddlecompany.com
If at first you don't succeed, figure out what went wrong, and FIX it!