Regarding your particular situation, I think Axioplase, Mark and Istrasci have given you all the options you really need. By order of smoothness, I would go with:
あなた (as Mark says, there's a bit of cognitive dissonance between the two uses, but it still works)
To answer the more general formulation of your question title, I would add one that I personally found a lifesaver in many similar situations. For people you want to be polite to, but don't want to use 'あなた' with, for some reason:
While it is not ultra-common use and practically keigo level of politeness, it is still somehow neutral enough that using it in semi-formal conversations (typically in my case: people slightly older/higher, whose name I forgot and whose meishi I misplaced, but for whom あなた sounds a little too precious) is perfectly alright.
Edit: A very typical way I would use そちら, is if, after making a sentence omitting the subject (my first choice), there is an ambiguity and/or misunderstanding. As a way of saying "you [not me]".