Thanks for the responses.
Vertex, I'd not seen that; thank you.
Scottbombedout and Earlofsodbury, there is a mobile phone mast nearby and quite a lot of wifi. In addition, much of the building is glass.
The intention is to reduce such exposure. This is also advised by my medical doctor.
As to how much to spent, I think it more of reducing exposure perhaps by screening the bedroom in particular and cost effective steps in the study and even living room.
It's a rented property abroad so there would be limits to what could be done. Eventually, I'd also like to do things to home in the UK.