Addendum:
Google Wallet can of course also be called up using gestures.

I consider gesture control to be one-handed. If the watch is worn on the right arm with the prosthesis, you can use your left hand to control the gestures in the 4 directions. The watch can be set to be worn on the right arm. You can even determine which side the crown should be on.
The heart rate actually works continuously. Not all smartwatches can do this.
Google Wallet can be installed on the watch. Preferably on the smartphone first. Then it synchronises itself, provided this has been set up on the smartphone (Android). Google Wallet can be activated by quickly pressing the crown twice. The payment card will then appear. The payment function at the payment terminal works very quickly and at a distance of just 5-10 mm. Better and faster than with the card. The payment card (e.g. Visa Debit) must be activated via e-banking in the card settings for online banking.

I assume that you want to operate the watch with one hand?
This is only possible to a limited extent. With the display always on, the time can be read at any time.
With a short turn of the wrist with the watch, it "wakes up" and is active to react to touches on the display.
Various functions can be activated with swipe gestures (left->right, up->down and vice versa) on the display. However, this is already a two-handed operation. Pressing the crown also activates the display and there is a small button next to the crown to call up frequently used functions.
The heart rate measurement works well when the watch sits snugly on the wrist.
I don't use the payment function and therefore can't say anything about it.