You might ask your veterinarian if he would be willing to add 10 drops of Dia-IonX to the food with breakfast and supper. Does your veterinarian think your cat is very stressed which can make the blood glucose worse? I think you need to talk with him some more to determine what would be best for your cat. It is difficult for me to make a recommendation about hospitalization for a kitty that I haven't seen or worked with. Perhaps fluids might be needed as well.
Please keep us informed of any more information you get and we can talk about diet and supplements once your kitty is a little more stable.