I looked at a bunch of different saddles and the brand that seemed the least expensive, but came in many sizes for a almost sure fit was thorowgood.
I was reading the description for each saddle, and I think X would be better in a ordinary T4 GP, but I'd like opinions.
T4 GP(description from website): If your horse is neither low nor high-withered, more of medium withered shape, middleweight horse then this universal fitting saddle is the answer.
Or the T4 High wither GP: (description):
> Tailored for high-withered horses, such as Thoroughbreds and Warmbloods, with tree and panels specially shaped to give maximum wither clearance.
Now X's withers aren't high, so I suppose even if he is a Warmblood, the GP would be better than the high withered, right?
Here are snapshots of him: