Having a good saddler is always the best idea. Check yourself first, is the saddle (English - western is not something I am familiar with) is clear enough off the withers (at least 4 fingers when you are not mounted). If everything fits here, check that the saddle is not put to be hit by the scapula while working. If everything fits here too, check the horse's back by sliding two fingers along the spine's sides, on the muscles. Start at the withers, end at the thighs, putting an even pressure but don't drill through the animal. If he shows signs of yielding, something is wrong and you should get a chiropractor and get your saddle checked, as it usually is a result of an ill-fitting saddle or one having the filling uneven and bumpy. But, if your horse doesn't show any signs of pain in the back, we go back to point 1, the saddler. I wish you both all the best!
My horse has a very high wither so I use a riser pad which really helps!
hey. make sure your saddle is fitted properly you can also get special half pads that will help keep the pressure off the wither. horses have many pressure points in their wither so if the saddle is fitting properly. thicker saddle blankets with more puff my also help