I am a dressage reder ustabe: now I ride Western for a variety of reasons. I can't stand depending on a mounting block or another person for mounting because I fall off all the time. But you have to bounce, and then trying to be as light as possible, kind of lean gently over the saddle once you are up. I HATE it when the saddle slips! Also, if you use a handful of mane, that helps.
Using a mounting block is easier on the horse, though. My most embarrassing Western moment re: saddles happened just recently. I was trying asaddling method that a friend showed me, where you swing the saddle back and forth, ant then gently swing it into place up on the horse's back. I was doing this, but my saddle is a heavy Black Rhino, and I lost control... The whole saddle went sailing through the air, barely missing poor Ahab.
He just stood there, looking at me, like, "You are such a moron!"