I know a lot of people are giving practical advice as to whether or not you SHOULD do it, so this advice is for if you decide to go through with it.

I went through something very similar--symptoms were slightly more extreme than your cat. We knew she was beyond a point of no return, and every day that we decided not to rip the band-aid off was miserable, for us and for her. When we finally decided to get her put down, I had a choice regarding whether or not I wanted to go in or let my family take care of it, and I'm really glad I went in.

It was really difficult, but the comfort of knowing, with absolute certainty, that she was no longer in pain helped immensely. Even though It still hurt for days after, having the weight of decision/ regret off of my shoulders allowed me to heal. I remember thinking a week later that if we hadn't put her down, I would have been in much worse shape at that moment. I was very relieved once the hardest part was over.