Well, you've gotten lots of great advice already! I would start looking around. It may be difficult, though, to see those cute puppies and not be able to take one home immediately! You will start to see, though, at what age the puppies start to be chosen, with deposits placed on them, and plan backwards from your projected date of bringing home the puppy to when you should really start to look seriously. In the meantime, seeing breeders, their parents, and puppies will get you off to a great start! And some breeders may tell you have they will be expecting a litter that will be ready to go home in the fall.
I commend you on being so thorough and so prepared. It sounds like you are doing lots of great things to be ready for a Yorkie.
Perhaps I shouldn't say this, but I did have a thought... What if you continued to lose weight...and what if you started looking around at different breeders...and what if you fell in love with a puppy that would be ready to go home before the fall? Would it be so horrible to get it early? I'm thinking that your puppy could be a great incentive to exercise! By setting up a walking schedule, you could walk your puppy two or three times a day - nice, long walks, which will help you reach your goal, and will be great for your dog's health and behavior! Just a thought... I don't want to make you break your deal, and I give you so much credit for being so disciplined!