I think it is great any Yorkie owner studies the nutrition they feed their dogs, they will learn alot.
Here is the food I feed my dogs and I do the raw diet and they love it.
http://www.naturesvariety.com/
If you do a search on YT you will see many threads on this topic but my best suggestion is for you to know what could harm them and to read the labels. Sorry to say, most vets (per my vet) have had very little training in vet school on nutrition. Of course years ago (maybe still true) medical doctors didn't have indepth training either. If I remember you are a nurse and you would know this better than I would.
Good Luck in your search as I know you will do what is right by your little one.