Re:
I really feel for you, I'm in a similar position myself with my dog, big C again. He was diagnosed purely by chance when he was in for a checkup three years ago.
He has now had numerous operations but last Christmas they said there was no more they could do. He seems fine up to now , but it's just a matter of time. I'm dreading having to make the same decision you just have.
I have to agree with Mike's comment above, although another cat will never be a replacement for Michah I think it would lift your spirits, you can't help but laugh at their antics.
Take care,
John.