Thanks for the detailed advice Pholi. There's no mention of squats as a substitute for PFE in Hold it Mama although she does recommend practicing in many different positions as you improve. There's also quite good explanations of how to make sure you're doing it right. I think this is what worried me most as most advice I've read just talks about doing the pee stopping exercise as if that's all you need to do to be sure you're using the right muscles.

I'm not sure if I'm unnaturally obsessed with this topic at the moment - I've only every had very occasional minor sneeze/laugh incontinence. I think I'm most hoping that PFE will help improve my chances of an intact perineum. I figure the more aware I am of those muscles now the more chance I have of being able to keep them relaxed during second stage.