Even the 4 lb variety. Mine are 4 and 5 lbs, and the things that I do to be sure they are happy and healthy from a size standpoint are:
1) Make sure I dont step on them; they are always getting under foot as the love us almost as much as we love them!
This is really only an issue when we have guests. They may not be used to looking down at their feet all the time when ever they shift positions or get up. I am always reminding guests to LOOK OUT FOR YORKIES underfoot!
2) Be sure that there are doggie stairs in strategic places around the house. Sometimes they try to jump higher than they should, and although its probably OK, I get worried that they will hurt themselves, so we use those doggy stairs you can buy. One for a couch in the living room and one for our bed.
I would never want a yorkie to be too small to get up and down stairs in a mulit level house. Mobility is key to their happiness and I already carry them a lot so they dont have to go down the stairs, but they are big enough to do that when they want to. If they were much smaller (2-3 lbs or smaller) I'd be scared that they could injure themselves, particularly if we weren't around.
