I reached out to Jacquelyn at Stampede Saddle Solutions in the hopes that she could offer me some suggestions for a saddle for a "hard to fit" horse. Chieftain is a 5yr old wild mustang who is extremely wide, flat back and low withers. She confirmed that my western saddle was not a good fit which was backed up by issues I was seeing in my riding. 

She was able to give me a couple options based on different budgets and provided detailed information on each saddle which helped me decide. 

I chose the Arena Wide All Purpose saddle which has an interchangeable gullet which will be extremely beneficial if my horse has not yet reached maturity. 

The saddle is extremely light weight and looks very professional. My trainer took it for a test ride and we watched in amazement as my horse moved more freely and athletically than we had ever seen him. My trainer described it as "best ride to date".  I have now had an opportunity to ride in it and cannot believe the level of comfort. The saddle fits my horse like a glove.  Does not move or shift even in riding trails and hills. 

Thank you so much Jacquelyn for all your help and expertise with this process.