First, Good for you for riding your bike. Every woman I know who has dealt with breast cancer had found her bike a help during and after treatment. (This may have to do with the kind of people I tend to hang with). I know that my bike helped me - I rode to the chemo treatments and to most of the radiation. Yes, pride was involved, but it helped my mental health as well. I know another woman on another forum who either walked or rode to treatments for the same reason.
I agree on making or having something made Just For You, especially if it is from your Mother in Law. the love your MIL puts into the tanks will be a source of strength - and my bet is she will be happy to Do Something for you.
On going without the breast forms, I doubt anyone will notice while you are riding. After all, you will be passing everyone in sight, being so much lighter, right?
You can always use the forms when you are dressing up for a night on the town. You aren't stuck with one look. Do what works and makes you comfortable with yourself in each specific situation.
On the same topic, I'm trying to figure out how to deal with the fact that I'm now lopsided. My doc took quite a bit from the affected breast, amounting to breast reduction surgery - but only on one side. Buy two bras to fit the different sides, cut them apart and sew them back together to fit? Seems wasteful.
Give big space to the festive dog that make sport in the roadway. Avoid entanglement with your wheel spoke.
(Sign in Japan)
1978 Raleigh Gran Prix
2003 EZ Sport AX