My old cat is getting worse. He keeps losing weight little by little, and I can only hope that the sore on his face doesn't progress.

The vet advises against switching food due to his old age and allergies (which lead to the sore). However, I have not been able to feed him his usual dry food since August. I've been searching for a replacement that won't make things worse, but with little success.

Not only he's fragile, but also rather cranky. :(