The stars and planets aligned, and I was able to get my vet, trainer, Custom Saddlery fitter, my sore-backed horse and me all together for an hour, and was able to find the right dressage and jumping saddles. The back soreness has never returned.
Now I have a half dozen Mattes pads and gel pads that I have no use for, plus six old ill-fitting saddles as tack room decor.