I assume you meant "gelatin". You can buy unflavored packets of gelatin - no need to give JELLO with the artificial coloring, etc.
Organic yogurt is also good.
I suspect you may be on information overload. Your vet probably gave you a lot of information and since you were worried about your baby just going through surgery, it was probably very hard to absorb.
Did you get written post op instructions?
I would call your vet tomorrow and ask your questions.