I agree with Karlin to maybe consider an older dog. You could introduce it to your current dog and better determine whether their personalities would be a good mix. Plus an adult dog is generally much easier to deal with than a puppy.
I got Gracie when my tricolour was about 7 months old. Gracie was 3 at the time but came from a breeder so she was very socialized and well trained. It took a bit of work for the first month for everyone to adjust but she fits in so well and is a well-behaved angel compared to a rambunctious puppy :).
Since your current dog is 6 and you don't seem to want to take on too much more work, an adult dog would be a lot easier than a puppy.
Also, I don't find that taking care of two is all that much harder than 1. It is twice the cost though!
I have 3 dogs. The first was a Japanese Chin and the second was a Japanese Chin, with the third being a CKC. From my experience, the 1st chin was thrilled to have a companion, and it certainly brought out a happier side to my first chin, which was a pleasure to see. Bosco, our CKC, is devoted to people, especially me. He will play with the Chins, but clearly prefers people to dogs. So, if you have just 1 CKC and your are happy with the present situation, and your dog is happy, I would leave things be. Having 1 or 2 or 3 dogs is not so much work, but the dynamics of the pack interest me very much. I think chins need other chins, but I think a sole CKC would be just fine.
We got a rescue when Brooky was two...I was really worried as Brooklyn was our whole hearts. I knew I could not handle another puppy, and prefer a dog past that phase now ;) but we got Toby a boy who was 6 (Brooky is a girl).
I will tell you...to be honest...we were totally sure if we wanted a second when we adopted Toby, and that made it a LOT harder to adjust to everything. My situation is a bit different as Toby came with a lot of medical and behavioral issues, but after we figured out how to make it all work, about a month in, we are very happy. But it did take adjusting and in my opinion, two is harder than one for sure...but I think this really depends on what kind of person you are to feel if two is harder, the same or easier.
What has been amazing is the relationship between Brooky and Toby. I could never imagine not having another dog for Brooklyn now. They enjoy hanging out alone when we are gone now, snuggle, play and seek eachother out when the are nervous etc. they joy and support I think they give to eachother is priceless. But as others said, you have to be ready.
Rescuing or getting an adult dog does take out all the heart ache of potty training, chewing, training etc! Toby is SO good, it was instant in terms of "house rules". :)