Hi and welcome to YT
! It's always so wonderful to see people who are willing to do the work and research *before* buying a dog or any certain breed - that's just awesome bc it will make you the best pet owner in the long run.
You've already received some great advice, but I just wanted to say - don't be too afraid of a 4-pounder. I have 2 that are in the 3.5-4lb range and they are very sturdy little beings, you might be surprised. The standard for yorkies is under 7 lbs, so they're all going to be on the small size...but 4 pounds is still very doable. If you really liked that breeder who had the 4 pounder, I'd give it some extra thought maybe?