I like the Bates Innova, I didn’t notice too much difference comfort wise with the monoflap but my former trainer (who rides in the mono normally) likes the mono more.
I have whole system joint problems but if I need to treat it from the ground up or else I do feel it in my hips and back (very problematic hips - open joints, prior trauma, regular subluxation, something yet to be determined sticks with stairs or if I sit funny, etc). So jointed stirrups, really pay attention to knee block and stirrup bar placement, moderate seat (I don’t find Bates that deep or shallow personally), narrow twist, etc. My PT lectures me regularly on warming up off the horse and stretching once off since that really isn’t part of the normal riding culture (I know the BNT are shown getting physio before they ride but for us normal people, not so much).
I really do do better with narrow horses (did really well with a horse that was generously described as a 2x4) but with the above set up, made it work for a very round, pregnant ISHxArab mare.