Continual poor connection within parts of my home

[Daniel8282]

There are only 2 rooms in my house that seem to have good wifi connection. 1 has the modem box and the other is the room directly above that. 
I struggle to stream or connect with devices in any other room. This is a situation that has worsened over the past 3 months but was not experienced before that. 

[Highlinder]

@Daniel8282  Have you changed any of the hardware recently in those few months?

[Daniel8282]

I had sky glass and a new router installed 9 months ago. For 6 months it's been great but for 3 months the performance has degraded significantly. Now unless I'm within 1m of the router, I get buffering etc. 

Sky inform me that the hardware is working fine but I now need a booster at £10 per month extra! Seems odd when you consider the system was working fine 3 months ago but now unless I'm with 1m, it's performance is terrible.