Speak to your vet. They actually love animals. Don’t just presume your dog is in discomfort.... ask.I don't have advice, we're in a similar position.
Our cocker spaniel is 15.5 years old and struggling. She's deaf and her eyesight is terrible now. She's not off her food or drink, and doesn't appear to be in any discomfort, but she also doesn't seem to have any joy in life any more, and I think she has dementia (she doesn't really know who we are ). She's been an amazing loving pet, she's never so much as shown her teeth at anyone, despite years of having her fur pulled by toddlers etc. Now she's not easy to look after (regular ear and eye cleaning, and she goes to the toilet inside more than out), but I don't want to put her down just because it would be easier for us.