I am going to offer a different approach here.
Yes getting another Yorkie may help because it may distract your dog from the fact that you are gone, but it may not.
Many people largely mistake the true meaning for "separation anxiety". We think our dogs are sad that we are gone, and that they miss up and they want "Mom or Dad" to come home. This is a totally natural response but, the total opposite of the true meaning for the dog's behavior. In reality, the dog is distressed because you are gone, that much is true, but not for the reason we think. It's upset because it does not know where you are, if you are safe, and it does not know what to do. In simple terms the dog views you as it's "child" and you are it's full responsibility. So it is simply panicking because it does not know where you are and if you are safe. It believes itself to be your alpha which means it believes to be in control of you and to be your leader. Though your Yorkie may not look like a wolf, it still thinks and behaves exactly like a wolf, so to understand dogs and their behavior, we must understand wolves. The reason this may be popping up now is because your dog is maturing (9 months old right?).
Simple tips to try and correct this:
Instill in the dog's mind that you are alpha. Once the dog believes YOU are it's leader and YOU are in control it will not panick when you are gone, it will simply believe you are out on a "hunt" and wait for your return.
There are four meaningful times you must always underline your alpha status.
Greetings:
When coming home, or coming from outside, or coming back from any separation follow these rules. Also, a "separation" has a different meaning to you dog. To them it can be you simply closing the door behind you, blocking them from you for only two seconds. Basically it occurs when you erect a physical barrier between you and the dog.
-When you come back from the separation, IGNORE YOUR DOG. This is very hard to do at first, as we have it set in our minds that we should greet our family, but keep in mind, they operate on a totally different language. Make no eye contact, say nothing, and go about your own business. Your dog may bark at you, trying to get your attention, may jump up, etc, keep ignoring. Ignore your dog until it leaves you alone and relaxes. This is signalled by the dog walking away and laying down, or going off to play with a toy, etc. After that happens, wait at least five minutes, keep ignoring this dog during this time. If the dog comes back trying to get attention again during the five minutes you must start all over, wait for it to relax again, and wait another five minutes. Some dogs can keep up the "give me attention now" thing for a very long time. After a full five minutes (at the LEAST) has passed without your dog trying to get attention from you, then you may call the dog to you (do not go to the dog) and when it comes to you, give it all the love and affection you want!
TIP: ALWAYS call your dog to you for affection. Never go to the dog.
Feeding:
Do not leave food out constantly. Feed at certain times, and before setting the bowl down for the dog, pretend to eat out of their bowl, eat something as small as a cracker, just make sure it looks like it came from their bowl and make sure they see you eat it.
You Lead The Way:
Always go outside before the dog. Always cross a door threshold or narrow hallway before the dog. Always go up or down the stairs before the dog. Apply this rule to everything. You lead, always.
Do these things, and follow these rules strictly. Always ask your dog for affection, do not give it affection when it asks. You always ask, because you're alpha, not the dog.
If you succeed in teaching the dog you're alpha, the dog will feel that you are in charge or it and that you protect it and therefore will be much happier and relaxed because it will feel safe and worryfree.
