I don’t know if this will help.
I am riding a 28 year old Appendix QH. There is nothing that “screams” that he needs any special type of pad. However his sitting trot feels like I am trying to sit on a jackhammer so I experimented.
Right now I am using a Fenwick Western pad with a ThinLine Contour pad on top of it. I am doing a Western pad because, like many of the lesson horses, he had a “hitch” right behind the saddle that interrupted the flow from his pushing hind leg. The Fenwick pad is no longer made (there still may be a few on the Fenwick site, on sale) but there are other Far Infra-Red Radiation Western pads out there, like the BOT one.
He obviously likes the Fenwick pad, that hitch behind the saddle disappeared, but his back was still so stiff that I totally refused to sit his slow trot. Adding the ThinLine Contour pad made a LOT of difference in how happy he is about being ridden, AND he is finally warming up to me when we tack him up, plus now I can sit his trot–some.
For any horses I run into whose backs have a fitting problem I also got the ThinLine Trifecta six pocket pad and the ThinLine shims, and I would be using the Trifecta pad on top of the Far Infra-Red Radiation pad. I was going to try this on the other very elderly horse I ride but her owner is suffering from a badly done gall bladder surgery at an out-patient surgery clinic. It may be months before I can use this set up.
Six pocket shimmable pads are simply wonderful. I ride lesson horses and I cannot afford to buy each horse I ride a properly fitting saddle. The six-pocket pads with shims really help to make both the horse and I more comfortable while riding, and with intelligent usage of the shims can help make up for the fact that the saddle no longer fits well any more.