Join Date: Oct 2011
Location: Illinois www.saddleonline.com
I've had good luck with non-slip pads, though I'd be wary of rubbing with a non-slip girth.
Since your saddle fits, I'd say you just need to make sure to get the girth as tight as possible, use a tall mounting block and possibly even have someone hold the opposite stirrup for you while you mount, if someone is around.
Mounting quickly with agility will also help, the more time you spend pulling on one side of the saddle, the more likely it is to slip.
A breast collar is not going to significantly improve the situation - if anything, it may irritate your horse by applying additional, uncomfortable pressure as the saddle slips. Your breast collar would have to be extremely tight before it would do much of anything for slipping. A back cinch would slip right along with the front cinch.
"Riding: the art of keeping the horse between you and the ground."