I ride this wither less horse.
http://i1122.photobucket.com/albums/l531/purpleorchid102/IMG_0683.jpg
I ride her in a wide Solstice, 18", I think it is a 32cm. ?? But I know it is a true wide.
I use a toklat wool back double elastic girth. Double elastic keeps the pressure of the girth equal on each side. I girth her on the first and last billet. The third billet helps keep the saddle better in place, imo.
For a pad, I use this pad. No slipping or less than 5% slippage. That is if she is SUPER sweaty, and we are doing really hilly terrains. This pad works far superior than anything I have used.
http://www.smartpakequine.com/newmarket-handy-pad-8191p.aspx?cm_vc=Search
And, since my mare has a sensitive back I got a Mattes half pad, fuzzy only in the front but not the back.
http://www.smartpakequine.com/mattes-half-pad-dressage-7283p.aspx?cm_vc=Search
I can not use a plain cotton pad. It slips. I can not use my very nice wool back pad, because it slips. Also it is too much padding/bulk, which causes slippage side to side and the saddle goes back. No poly/nylon or flannel, they slip. She sweats, and they slip all of those slip. And I have tried an equipedic, well lets just say STAY AWAY. This pad slipped the worst of any pad in my whole riding history, which is ummm, a good number of decades.
I have learned how to ride a witherless, mutton withered horse. I do try to keep my horse as slim as possible. The saddle is really important to fit right.
I do ride on hilly areas with a breast collar. It is a beta breast collar I got from Long Rider’s Gear. But I do not use it unless I go on a hilly terrain.
I ride this horse a little tiny bit in the arena 2%, and 98% of the time on hilly trails, and a variety of terrains. I do not ever use a crupper. My saddle never ever slides back that far. Her ribs are there to prevent that.
With my current set up of the saddle and pads, I feel confident I could go and pen cows, or cut cows, or work cows. So, this is a secure set up for this horse and this rider.
Ok, my .02.