Dog fur prone to knotting?

[venus_smrf]

I have a yorkie/poodle mix (at least I think that's what she is), and her fur is very straight, very thick, and very fine. It's beautiful, but it knots insanely easily. I spent hours every day combing her out, but by the next morning, she has just as many new knots. I really don't want to have to cut her fur short, mostly because I love the black fluffball look she has now and also because she'd look like a rat with short fur. Still, I'm losing this battle, and something has to be done. I already condition her fur every time she gets a bath, and I have a pet detangler/leave-in conditioner for after, but it's clearly not enough. What else can I do?