I have 2 pads I like a lot and my horse does too. The one I use the most is a Skito pad and the other is a Cavello Old Mac pad. Both are pretty thin. I like the Skito because I can take the inside out and wash it. Both of these pads are kinda expensive in the $100 range, not the top end Saddleright but good pads.
I use just a plain navaho pad.. I wouldn't know where to buy one since I got mine from a friend, but its pretty thin. I don't have a western saddle anymore so I usually work my gelding in my all purpose saddle and borrow my trainers show saddle for shows.. But the pad is definitely western I think its called a navaho pad... its a weaved pad.
Is it some kinda synthetic (neoprene or whatever)? I did buy synthetic no-slip pad this weekend (hell expensive with padding here and there etc.). The only reason I decided to try it the woman in store said she rides barrels on all her horses with this pad, and they love it. So I tried it on my horse. Well... To make long story short my qh bucked me off in 2 mins (she was really bronco). So I assume it doesn't work for her. Lol!
Kitten, my horse hates those tacky/neoprene pads and will bite at me if I put one her, I think she is actually biting at the pad. The skito is fleece on the underside and it has a memory foam type stuff inside. It has velcro along the top you just open and take out the inserts and wash the outside. I've washed mine several times and its back to just like new. I have a rounded skirt saddle and the pad is rounded, if you have a square skirt I'm not sure if they make one but you could check.
The Old Mac is felt on one side and neo on the other, its reversable. I never use neo. Side, for reasons stated above, always have the felt side down.
Here is a Skito, not mine but from a web site. Mines in the tack barn and its too cold to go get it. They come in many different colors. I found a pic of it on Vida so will add it. Taken last week on a trail ride break :)