Put a chamois under your saddle. Much cheaper than buying another piece of tack, works better, and isn’t “out of fashion”. In fact, nobody by you will even know it is there. This is what is often used on racehorses (how well do you think those little race saddles stay in place at full speed?). The classic is the real lambskin ones, but mostly people use the tacky stuff that goes under a tablecloth, which works just as well. Dampen it before putting it on. Pull it up to get any pressure off the withers before tightening the saddle. You can purchase one at any racetrack tack store for a few dollars.
I always feel that if a breastplate gets tight enough to actually HOLD the saddle forward during the jumping round, the pressure and restriction on the shoulders and chest is not something that I am looking for for my horse. The chamois works well.
