Generally, the stability of a 2-wheel vehicle is guided by the wheelbase and center of mass when the vehicle is in operation.
The longer the wheelbase, the lower the center of mass is located on the 2-wheel vehicle, the more stable it is at lower speeds.
LWB recumbent with battery mounted between the wheel axles is like the most stable for 2-wheel platform, but at the sacrifice of handling, not the quickest.
Sitting lower to the ground level obviously helps with putting your foot down quicker.
For cruiser type bicycles, the long wheelbase and steering angle contribute to its stability, more over the balloon wide tires & large diameter wheels.
Maybe not the most efficient platform for e-bike, but certainly not difficult to manage or to balance.
If OP still prefer sitting upright but have balancing limitation, maybe an e-trike is also an option.
My in-laws are in the 80's with balance issues, I bought them a Lectric XP Trike for $1500, they've been able to enjoy it as much as the fat tire e-bike they used to have before the pandemic, when they had less balancing issues.
