I would try a Stubben. I love the Tristans because they aren't as deep a seat as some saddles. (I have a Stubben.) And I also recommend trying a Duett. I just purchased one for my fat little Arabian mare--an all-purpose that rides a helluva lot like a dressage saddle--and it's suuuuper comfy. In fact, I like it better than my Stubben, and so does my mare!

A thought on your pain issue. I have nerve damage on the left side of my bod, and it's a b!tch to deal with. I've tried all kinds of things, but one option that works more often than not is acupuncture. It seems like voodoo, but it really works. It obviously won't fix the underlying problem, but it controls the pain, and that's what matters.