I also was afraid of making the crate as a negative place for my yorkie
what has worked for me is: whenever he bites me (even in the slightest way), I give a high pitched yelp (like another puppy would) and then i turn my back to him and ignore him for a minute. He now knows that i don't like that kind of play.
What's really cute is when he forgets and is about to nip me, but catches himself, closes his mouth, and licks me instead
