I am so sorry for what you are going through.It's devastating to contemplate your beloved friend suffering and to imagine life without them
I lost the feline love of my life 15 months ago..he had just turned 16 . As hard as it is for us, we have to do whats best for them.It's obvious you love your baby very much and want to spare him stress and suffering. There aren't a lot of pain alternatives out there for cats , one that is safe & commonly used is Buprenex ( buprenorphine), my 13.5 year old cat has small cell lymphosarcoma, and is currently taking Buprenex as needed. he has been on chemo medication recently ( leukeran), which while it works for some cats with minimal side effects and they can go onto remission, in this case it caused him to be very nauseous and lose appetite. and weight. So I have stopped the chemo and am giving him his other meds. I, like you want whatever time he has to be as pain and stress free as possible the Buprenex is in liquid form,given by mouth from a syringe, they are given a very small amount so it's easy to administer. I get mine from a local compounding pharmacy who are able to flavor it so it is more palatable ( it can also be order on-line from a compounding pharmacy) I would ask your vet if Buprenex would be appropriate for your cat, the only major side effect I am aware of is potential for constipation but there are things to counteract that if that proves to be an issue ( over the counter Miralax in their food, Cisapride by prescription), my cat is on both. I would avoid Metacam at all costs, if the vet mentions giving him a pain injection be sure and ask exactly what is. Metacam can cause sudden death or serious side effects in some cases. Onsior is safer but is generally just used short term , i.e after a surgical procedure we sometimes have to assume cats are in more pain then they manifest, cats are very good at hiding pain and weakness. My best to you and your baby Diana
Bee- "Good night sweet prince & flights of angels see thee to thy rest"