Aha! You've gotten bitten by the "can't have just one" bug.
I have one Yorkie and two Biewer a la Pom Pons. All came to live with me within 6-7 months of each other (the last coming this past February). And they are each 6-7 months apart in age, with the oldest (Yorkie) turning 2 in Sept. and my littlest guy turns 1 on July 30th.
What I noticed immediately in my Sophie (yorkie) when I brought home Ivan (Biewer) is that she quickly "grew up". She stopped being the PITA, look at me, play with me, talk to me Yorkie and became like a big sister. The potty accidents stopped, the chewing on my baseboards stopped. All the bad behaviors stopped.
And when I introduced Alfie (my littlest Biewer) I noticed the same thing with Ivan. He rarely missed the pee pad, stopped chewing on baseboards, etc.
There is an advantage to it all. However, they all three play and there can be more barks and tussles and arguments over the same toy or the same bully stick. It doesn't matter if you have 2 dogs and 300 toys/bullysticks on the floor for them. You can bet they will all want the same one! But that's the fun of having them.
Lastly, it boils down to temperament of your current Yorkie and the new one you may rescue. The Biewers are a pretty laid back, gentle breed. Adding them was no problem. My Yorkie remains my opiniated one and my Biewers just "go with the flow".
Good luck!