Redhook, the last dog I had to put down I should have put down a week before I did, but I didn't want to feel like I hadn't done everything I could. But here's the deal. My dog wasn't feeling better, except for very brief periods, and it was expensive, emotionally draining, and expensive. It hurt to lose her. But looking back, I realize that I was wrong to keep her alive past her time.
Putting her down was painless for her and I held her as she died.

It's all your decision, and I respect your efforts and hope for the best for you and yours, but it may just be your cat's time to go to sleep and not wake up. Give it some thought. There are lots of critters out there that need someone to love them. Maybe your time/money would be better spent on one or more of them?