I have two no-wither, forward girth groove, perfect for bareback riding mares. I hate having much of anything between the saddle and horse and started with the BOT Thinline combo pad which works very well without being too bulky. But better yet is the Mattes full pad. Yes, expensive and you wind up having to wash with Melp(?) but definitely still feel very close to the horse and more stable side -to-side and front-to-back. I also got the TSF girth which helps with the forward girth groove.
That said, has anyone tried the Sedelogic pad that Dressage Extensions is promoting? I think it would be too thick for the mares, but might be great for my aged Thoroughbred. Here is the link.
http://www.dressageextensions.com/sedelogic-half-pad/p/2643/