I agree with barneysmommy
It could be a good thing but then your little Chester may be jealous since he has been the center of all your affections.
I had three older yorkies and they were very close. Then in one yr I lost two of my sweet little girls leaving my little male Beamer.
At the time Beamer was about 12yrs old. I had been depressed over loosing two special girls and I wasn't sure I was going to get another. Beamer was grieving for Bree one of the girls we had lost because they had been raised very close. Like you I was trying to make the right decision about introducing a new baby!!!
To make a long story short we did get another puppy a little male who happened to be very loving and gentle and adjusted to Beamer quickly. He actually would lick little Beamers face and lay close to him in Beamers bed. So it was a good thing for us because Beamer seem to enjoy the company. We then got another female who came into our family and they all got along sooo good. It could go just as good for you too. I think it depends on the personality of the puppy you get also..
Since this is a good friend maybe there could be some get acquainted time for your little Chester and the puppy with your envolvement.
I'm sure your heart will lead you through this time of decision and you wlll know whether little Chester is ready for a new buddy.