Have read your initial post but not the whole thread (will do in a min) anxious to share my thoughts. I'm an oldie owner (18 and 21) so may be able to help.
I don't think there are any kidney problems as you don't mention drinking too much water.
Has your cat been wormed recently?
The coldness indicates poor circulation, probably due to the lack of movement. This may be related to some kind of joint or muscle problem such as arthritis or rheumatism.
The vomitting immediately after meals and the white frothy bile is indicative of a blockage. Treat for furball. This is often my first port of call as it can produce weird symptoms like the vomitting and reluctance to eat. The white frothy bile often happens when your cat has eaten grass and is trying to eliminate a furball but can't quite do it.
Personally I'd
1. treat for furball
2. worm with vetinerary pills
3. see vet about joint/muscle problems and any possible relief for this.
4. don't regard your cat as 'passed it'; your cat doesn't think like this.
5. give your cat occasional tuna IN OIL, maybe once a week.
Hope this helps.
Oldies are great!