Personally, I've found most of my rubbing/chafing problems comes from riding with a poor seat or in a stirrups that don't fit. I've never really had any problems with clothing or saddle surface(smooth vs. rough) causing any issues, but I do have plenty of issues if I've injured myself and I can't ride with as good of a seat as I normally do, or I have to swap saddles/horses fast and don't have time to adjust the stirrups to the length I need them. I ride western as well, and have no problems switching between my normal saddle, smaller saddle, or roping saddle(which is slightly too big for me), but stirrup length will make a huge difference, as well as posture/seat.
If you have a trainer/good horsey friend, I'd personally ask them about your seat/posture just to check and make sure you're not making any mistakes, and then go from there on what might be wrong. Also, try messing with your stirrups. I couldn't sit the lope for days for some reason one time, and then I decided to check my stirrups and found them a whole 2 or 3 holes higher than normal(my horses make it around the block and I have some younger siblings that ride occasionally). I dropped them and miraculously, I didn't feel so awkward trying to sit the lope(which, given my smooth mare, should be easy). ;)
"The art of riding is hard to find and easily lost."