You probably need another layer over the knickers... I know I do when it's chilly and it's not all 'that' cold here (50's?). That layer doesn't need to be wool necessarily, but if you don't want jeans you could wear a fitted pair of workout pants or something... or even sweat pants.

If you did choose to try jeans, you can get a reflective band to put on your leg on the chainring side, that would keep jeans from catching, however I've never caught jeans on my fx since it has a chain guard. My mixte with nothing isn't even all that prone to grabbing loose clothing as long as I'm not in the 'big' ring. you can always just roll up your pant leg so it's high enough not to catch as well... since you have legwarmers you'd probably be fine that way.