OK. What I would recommend is changing the controller to a current control one. Yours is a speed control one, which regulates the pedal assist to a fixed maximum speed, but gives maximum power from the start. A current control one would regulate to a fixed maximum current (=power) on each level, regardless of speed. On level one, the power is very gentle.
All controllers work the same in principle: Three wires for the motor, three for the throttle, three for the PAS,, two for the battery, etc., so you can use an alternative one.
If Wisper have a plug-and-play replacement with current control, that would probably be the easiest solution, but I've got a feeling that they only have current control on their latest bikes, so might not have a suitable replacement.
You will be able to add a throttle with whatever new controller you get. The half-width ones are easiest to fit as long as you don't have twist gears. After that a plain (no switch or LEDs) thumb throttle.
This one works quite well. You need the LCD, Speed sensor, PAS and throttle. Your present PAS will probably work with it, but for the sake of £2, you're covered. Your present brakes will be OK:
http://www.pswpower.com/peng/iview.asp?KeyID=dtpic-2016-3F-47MA.50CQY
This one would be easy to install:
https://bmsbattery.com/ebike-kit/647-s06pw-easy-assembling-waterproof-connector-kit-ebike-kit.html
and this one, where you have to order the LCD, throttle, PAS and speed sensor separately:
https://bmsbattery.com/ebike-kit/545-s06p-250w-torque-simulation-square-wave-controller-ebike-kit.html
Note: I'm assuming that your motor is sensorless (only three wires). If it's sensored (8 or more wires), you need a different controller.