While it may be too late to help the original poster, I'll leave this here for others with a similar question.
Adult training wheels/stabilisers don't work well. First off, even the biggest monster ones with 16" tires break. And that is on a non-electric! They simply can't withstand electric bikes.
Also you'd need to have them high up enough to allow the rear wheel (the one you pedal) to get traction, meaning the training wheels float unless you tip over a bit. It is not stable on an adult-size bike. Again, especially at e-bike speeds.
So where does that leave you? A trike.
Now if your balance issues are only with stopping and starting, but you can balance ok when you are actually riding, get a tilting trike. They steer like 2 wheelers when tilt is engaged, but lock upright when you need the stability. This means you don't have to lean uncomfortably and slow way down when turning or worry about tipping when you are on uneven ground. (This is the major downfall of most trikes and it's not easy, even if you are used to it). Most tilting trikes have two front wheels that tilt and one back wheel (tadpole style). But Bintelli makes a trike that is delta style (one front and two back wheels) that tilts. It feels like riding a two wheeler when tilt is on. (And just flick a lever to lock whenever you need)
Another option is a recumbent trike, which can't tip easily because it is low to the ground. Not personally familiar with how those feel to steer though.
If you need more than one wheel in the back, get a trike. Training wheels are not safe on adult bikes with any kind of speed or power.