I use a Mohair breast collar.. Frassy loves it! The mohair wicks the moisture better than leather or biothine.. Just like her mohair cincha. I agree that the use of a breast collar helps keep the saddle in place and lets you use less pressure on the girth area. Also I recomend the use of a crupper. When the horse gets accustomed to them they use them as tools when mounting, going up or down hills, and pulling downed tree limbs. When I mount or go down a hill I can feel Fras clamp down on th crupper with her tail muscle (one of their strongest muscles) to keep everything in place. I use them every ride, even short ones so the horse toughens the hide under the tail and learns to use it.
Here is Frass collar