Ziggy does have some high withers and large shoulders, there are a few people who make Gaited Saddles in a Medium and a Wide version.
The Abettas and Bighorns are for the wider Horse, you would probably have to go with an All leather Model, which are a little more expensive.
I would suspect he needs a Medium, but without measuring not 100%, he definitely would not take a wide.
Bighorn has one model that is a Medium/Wide that just might fit 16" Big Horn Brown Cordura Gaited Horse Saddle High Withers 257
Maybe your local shop might have that model to try out.