another thought might be to also try riding a bit on a stationary bike at the gym. Especially on an upright, you could practice sitting upright without holding on while pedaling. It will be more stable than trying the same thing on your regular bike, ditto practice mounting and dismounting. In fact, the bikes they use in the spin classes have clips so when I first got clips, I practiced clipping and unclipping without looking down, on a spin bicycle because I could just unclip and let one leg continue pedaling while I unclipped without having to worry about losing momentum and falling over.

Congratulations on your weight loss- been there, lost over 100 and still struggling with the last few, but know that my riding position, and sense of balance has definitly gone through a lot of changes and adjustments. Ditto the muscles and using them.

Hang in there, find a grassy plot, a friend, a gym and remember the only way to " get to Carnegie Hall is practice, practice, practice."