Sometimes, we are so close to the situation that we can't see it clearly. My girl was 14.5. She had DM, no muscle mass, couldn't hear, couldn't see well, was incontinent, had to be helped to her feet and have her rear lifted up the few steps into the house. She often seemed confused. Like you, I kept hoping she would go in her sleep. Sadly, that hardly ever happens. I found a vet, other than my regular vet, who would come to my home. Perhaps you could check around. If you find someone, get references. I can only say that after it was over, I felt a great burden was lifted. Incredibly sad, but I know it was the right thing to do. The vet came into my house and said, "Oh yes. It's time." I imagine people looked at my dog and thought, "Dear God woman, why don't you put that poor dog to sleep?" It is a very difficult decision that no one can make for you.
In my situation, it wasn't a new puppy coming into the home, but an upcoming surgery. I knew I would not be able to handle my old girl. Otherwise, I might have let her continue for a while, but to what purpose? I did not want to wind up in an emergency situation where I had to go to the Pet-ER and have her put down. That would have been traumatic for all of us.
A very wise young lady told me this....."It is better to put your pet to sleep two weeks too soon than one day too late." This is so incredibly true. I've been on the other side wishing I had not waited so long. Those are the times we truly regret.
I'm am so sorry you are facing these difficult decisions.