A friend has a room thermostat at the top of the stairs - not ideal for
sampling the temp - and he is getting a bit infirm.

I would like to help him fit a wireless room thermostat that he can have in
the lounge.

He would be wary of having his boiler wiring interferred with but I am
thinking that we could replace his existing room stat with a receiver. Not
sure if there are 2 or three wires - the house is late 1970's so I would
expect 3 wires (?).

What would be a suggested kit?