Water-pump controller is easy to get. Ours is made by CRI (pump manufacturers), I think V-Guard make one too. Of all the gadgets that I included when renovating this house, this is the most popular [with my wife

]. We never have an empty tank, and we never have an overflow, and we never have to think about turning on the pump.
The CRI sensor is non-mechanical (well, I am assuming that the switch inside might be a mercury switch) and simply floats, attached to its own cable. the on/off position is adjusted by sliding a weight on that cable. The connection to the control unit is thin wire, similar to telephone wire. Mains voltage does not (I think --- and hope!) go anywhere near the water tank.
It is possible to get a dual-sensor unit, so that the pump is not switched on if the sump (ground tank) is empty, but, anyway, there is a "dry-run" sensor that is fitted to the input pipe of the overhead tank, and the pump will be cut (and an alarm sounds) if no water is there.
I can add that it also just about the only gadget we have that has worked flawlessly for past three years!
Much to be recommended!