Kaileia,
Mitomycin effects vary, from none to considerable local discomfort in the bladder and when urinating, as has been reported here. I had it in combination with BCG and it eased the side effects somewhat.
Below is a link to an article, from a reliable author (O'Donnell) about T1 treatment. While the odds of recurrence are high, as you noted, the odds of NOT progressing to invasive can run from 52% to 67%. You are in a select group, with immune issues, so treatment and outcome are going to be hard to project. Five months is not necessarily "a long time" - If you are free of tumors now, you might be back to a T0 status - with a notation of prior T1.
The optimal management of T1 high-grade bladder cancer
www.ncbi.nlm.nih.gov/pmc/articles/PMC2792452/
While not directly addressing immune deficient issues, the following Clinical Trial report on treating AIDS patients with one of the newer drugs for a range of cancers.
Cancer and AIDS Keytruda clinical trial
www.cancer.gov/types/metastatic-cancer/research/hiv-pembrolizumab-trial
You may want to research open clinical trials that address your specific needs. Talk to your doctor about the above if they seem to fit your situation. Hopefully you find a treatment plan that addresses your specific situation and is effective.
Best,
Jack