Hey @Jools12 it is sometimes difficult to gauge peoples technical knowledge on forums, but as you know someone to help here is another suggestion. Powerline adapters!
They come with just Wi-Fi, or ethernet or both. They simply use your mains wiring to extend signal from your router to where you need it That way to get the best signal to say your TV you could use the ethernet connection, but for Wi-Fi only devices use that option.
Other suppliers are available, but to give you a bit more of an idea have a look on this Curry's page. https://www.currys.co.uk/computing/networking/powerline
HTH
