I am not into that type saddle, but wow is it very very very lovely looking. Looks sooooo comfy too.
Any pad you get pull it well up into the channel of the saddle.
I third a woolback. Pull it up into the channel as well.
Lots of times I use a thin cotton pad, and then the woolback on top. That way it keeps the wool back a little bit cleaner, and a little less wet. At the vet checks I like to put a clean fresh dry cotton pad on again. It just depends on the ride. Most of the time I use the woolback and not thin cotton pad. Just depends.
Any pad I get must be very very washable. Woolback is perfect for such wash and wear. I have had cotton pads wear out before the woolback.
I have the double elastic woolback girth too. Once again, very washable. Fluff with a wire dog brush when dry and wash. Or toss in dirty, either way comes out in perfect condition and clean.