My Equipe EKGO that is for sale won’t fit you (it’s a 17 with a long, straight flap), but it does work on horses like this. I used it on my growing guy when he needed more withers clearance yet a wider tree, and it worked ok until he grew into a beefcake. Which I knew would happen but he’d already grown out of the saddle I started him in.
A saddle like a Voltaire with a half pad doesn’t piss off a horse like this because the short tree points stay away from their shoulders. But Voltaire in general is not my go to brand for true high withers conformation. (Said beefcake is now going in a wide tree Voltaire but he no longer has relatively high withers compared to my other horse who does trend towards shark fin except when he’s morbidly obese and absolutely hates Voltaire after about ride 3).
Amerigo has a long head iron option that can provide some support for these horses without building up the front panel excessively. They also tend to work ok for some backs with some shape, which your horse has. World Equestrian Brands is the more centralized rep for both brands now, if you don’t have a local/regional rep near you. They have some used saddles and demos. You can also find some through the fitter network and on places like Highline, Goldfinch Fine Tack. I found my EKGO used through Double Oak.