I would be inclined to use Home Plugs. I use TP-Link ones with ethernet and wifi capabilities. You can also buy them with a pass-through socket so that you still have a socket to use for another appliance. You put one directly into a socket and plug your router directly into it (not via an extension cable is recommended). You pair up the second by plugging it into a socket near to the first one you have the router plugged into and then put that second one into another socket somewhere else in the house. You should then get a decent wifi signal and also a spare ethernet point should you need one, if you go for that option. There are quite a few examples available here.
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