I feed ours on raw food from a specialist supplier, they are carnivores, so is what they need. They also get a vitamin supplement, they don't need calcium as there are crushed bones in the mix. The food is human food quality, so perfectly safe. Unfortunately our fussy pair will only eat wood pigeon, they would rather starve than eat anything else! Raw food does have the advantage that the poos are firmer and don't smell.
But it is a very different texture, and I would not advocate changing an elderly cat over to raw food. There have been some good suggestions up thread, but your vet will probably give a few suggestions too? Good luck!