eero is considered one of the best wifi mesh systems out there. Three can actually supply them, they have some offers for broadband customers I believe in the three stores. They are available on amazon however if you have a Three store local i'd maybe pop in or give Three a call.
eero mesh Wi-Fi on Three | Whole home coverage and added security | Three
You can get powerline wifi extenders but my experience is, they're not great, i would look into a wifi mesh system like eero.
