All electric motors are high torque. What you need to do is match the optimum motor RPM with your wheel size and target speed.
If you are more concerned about power than speed, you could get a low RPM motor designed for a 26” wheel (say 200rpm) and use it with your 16” wheel. That is going to limit your top speed to about 10mph, but you won’t burn your motor up trying to run it at a speed that is too low for it to be efficient.
Torque really isn’t a problem, it’s just keeping your motor running at an RPM range it is happy at. If you are really worried about hills, you are going to want a high amp package more than high volts.