Originally Posted by Diamond Sutcliff
My instructor told me not to worry about the horse.
I assume she didn't mean not to worry about the horse and the saddle-fit on the horse. I'm hoping what she really meant was that you need to find a saddle that will be used on lots of horses - probably with some correction pads or shims as you move it around? I hope that's what she meant.
What do you mean by "the gullet size will change with the horse"? Are you looking for a saddle with the interchangable gullet system? If so, you have a better chance of making it fit several different horses. If not, then you'll need a shape and size that will just give you plenty of opportunity to pad and shim. So in that case, definitely avoid the Narrow tree size. Are all the horses the same breed or similar build at least? If so, you can find out what the predominant tree-size they need is, and target that size.
It would be better if you could ride in the saddle that is already fit to each horse, because it's impossible to get a single saddle to fit all horses. I'd be especially worried about this in a high-impact discipline like jumping. That saddle's gotta fit.
As for your height vs the seat size, it depends on your build as much as your height (long legs, no butt vs short legs, and curvy etc) and the maker and shape of the saddle. Some saddles are flat, giving you more room. Some are deep, giving you less room. I would think you could try out anything from a 16"-17". Try lots of them. They'll all fit differently.