I recently purchased a Zaldi. Zaldi are designed to fit Andalusians, which are also wide backed, broad shouldered, but have some withers. Their medium (which is truthfully what they call "average" meaning it will fit the average Andalusian) fits my Arabian wonderfully. A very different cut from the typical English saddle built to fit Thoroughbreds and Warmbloods. Morgans and Arabians are typically similar in build, so it might work for your guy.
Specifically, I got the Zaldi Royal, the AP saddle. Mine is 10 years old and in wonderful condition, so I can tell it was very well built, quality materials, and it's comfortable for me and my horse.