So sorry to hear your news. If you are not already, you need to be treated at a center that sees a LOT of bladder cancer cases; yours is not the "common garden variety" bladder cancer. Such places would be university medical schools, National Cancer Institute designated cancer centers.
Here is a very good very brief summary of the types of diversions available (a bag is not the only option)
my.clevelandclinic.org/health/treatments/12546-urinary-reconstruction--diversion
(If this does not show up as a hyper-link, just copy and paste it in your browser.)
A quick word on the diversions, the ileal conduit (the "bag") is the easiest surgery and often the only one that some urologists who do not treat a lot of bladder cancer are qualified to perform....which is why they recommend it!
The neobladder sounds good at first, but does have some issues; it is a long and difficult surgery and it works much better on males than females.
You have a lot of homework to do.....I recommend that you start with a second opinion at a really good bladder cancer center. If you need suggestions, post your geographical location and I am sure people will have good suggestions for you.
Sara Anne