@chestnutpony1 I am doing the exact same thing with a small horse built exactly like your pony. I will say that what you said are fat pockets on your girl is muscle on my boy, and they get more and more built up the fitter he gets which just makes the saddle issue all that much harder. I too am struggling to find a saddle that is large enough in the shoulder/deltoid area but small and curved in the seat. We have found a model he likes - Meyer shoulder free option, but haven not been able to find a used saddle small enough in the seat that has that option (not all Meyer’s do). They do make a pony saddle and I was told they could do the shoulder free option on them if you don’t find anything else, but custom will be very pricey. I can send you the rep’s contact name if you are interested. Good luck, I’m on saddle 24 and it is very frustrating. No saddles seem built for our horses/ponies needs!
