Hi and welcome to Yorkietalk! In the states, most good breeders won't sell a Yorkie before 12 weeks, because they are very vulnerable between that period, after they stop nursing. Learn about hypoglycemia and the symptoms to look for.
Dog Hypoglycemia (Low Blood Sugar): Symptoms, Treatment, and Prevention Steps can be a real problem and I suggest you carry up and down for the next few months. I even kept a gate at the top of steps because I was afraid my pup would fall. Carpeted steps are a little easier and they give the dog something to grip onto.