Problem: Poor WiFi signal on the second floor.
Best solution: Pull a network cable up two floors and add an AP.
Lazy solution: Test a mesh WiFi.
Google Wifi was just released in the UK, so I grey imported it and will give it a go to see how it performs.
Initial thoughts: WiFi coverage is considerably better. iPerf shows about 10 times increase in throughput between client on second floor and server on the ground floor.