Feline bladder cancer

I noticed that my cat, Amanda, who is just shy of 14 years old and has cardiomyopathy and the start of CRF was recently spending an inordinate amount of time scratching around in her litter box. I also had noticed she wasn't grooming quite as well as she used to (but it wasn't significant, and I attributed this to her aging).

Concerned about a UTI, I took her for her 6-month checkup a little early, and it was discovered she had lost 1-1/2 pounds in the last 6 months. The vet did a complete workup, including an ultrasound, and the diagnosis was bladder cancer. It looks fairly advanced to me on the ultrasound; it looks like the tumor is occupying 2/3 or 3/4 of her bladder. Considering her age and other health issues (not a surgical candidate at all), I have agreed with the vet to limit her treatment to meloxicam (similar to piroxicam).

Here is my concern: On the basis of my past experience with feline end-of-life issues, I always feel that I wait too long to euthanize. My worst fear is that my cat will suffer, and I feel that in the past, I have caused unnecessary suffering in my cats by waiting too long. OTOH, I don't want to rush to euthanize Amanda if she has any decent amount of time left. I know that if the cancer obliterates her urethral opening, it will become a medical emergency, and she will suffer greatly. I want to avoid this scenario at all costs. The vet wanted to prescribe enough meloxicam to last for a number of months. I told her that, given the size of Amanda's tumor, I thought she was being extremely optimistic.

My plan at this point is to repeat the ultrasound this week (one week after diagnosis) and see if the tumor has progressed. I'm also thinking about having a weekly ultrasound to track the tumor. OTOH, while Amanda is behaving normally at this point and is still eating and using her litterbox, she seems to have gotten frailer in the past week (or am I imagining this?). I'm debating about having her euthanized sooner rather than later (as in the next week or two), but then I'm thinking, what if she really does have several months left?

Has anyone had any experience with feline bladder cancer who can share with me how rapidly the tumor progresses? If the bladder is 2/3 filled with tumor, e.g., how long until a crisis occurs (weeks versus months)?
Thank you in advance.
Best regards,
---Cindy S.