I use a powerline system (TPLink) where you plug in a little box to the mains, connect the box to the main router, then plug the other little box into a mains socket at the other end of the house, then I hang a cheap wifi access point off it's ethernet socket. Works well. Basically, ethernet going via the mains power circuit from the main router to the wifi access point.
Similar to these:
https://www.ple.com.au/Products/6288...rline-1000-Kit
and this on the end:
https://www.ple.com.au/Products/6353...N-Access-Point
Note: they're Aussie dollars. Halve them for pounds.