Beautiful cat! going through the SAME THING it's hard. orange tabby just as skinny, not in pain, eats like a pig, everything functions...when they're this frail the chances of making it through are very slim. I did all the blood work etc waste of money he still lost weight vet just suggested changing diet GGrrrrr. The best thing keeping them comfortable they've lived a long life. Not sure if you do this but Sub Q fluids to hydrate can assist with disposing of toxins If you are considering that it's time but not sure measure the quality of life, good days to bad. Your vet can give you an idea what your options are by how well your cat's doing.
