Plug in extenders work very well, but may have to be located on the same wiring circuit in the home. WiFi extenders/boosters also do the job just fine although (as mentioned) they need to be located where the router wifi signal is strong enough to be of use i.e. not at the extreme edge of the router WiFi signal. I don't know the difference between an extended and a booster, and frankly, don't care.
I'm sure that the suggestion about running an ethernet cable is well intentioned, and in terms of network speed, is certainly accurate, however it rather misses the point. People generally don't want to install cables or mess with configuring a roaming vs extended network and that is why the other solutions are successful. You could spend a very long time wondering about the best way, or you could just pop down to Dixons or wherever and buy a cheap solution and apply it quickly and intelligently.
Good Luck