Join Date: Dec 2010
Location: southern Arizona
With that much padding, every saddle I own would slip somewhere. You need some padding in the front until you change the gullet...but that is about an 8-10 inch wide pad to fill in the difference between your saddle and the horse's shoulders. The riser pad NeuroticMare suggested has maybe an extra 0.5" of padding in the front. It doesn't take much.
If it takes more than that, you need a different saddle.
You can also try a different material for the saddle blanket you started with. Some of the English-style blankets are slick as snot on a doorknob.
"Make the right thing easy and the wrong thing...well, ignore it mostly."