Since moving to our new house, I haven't been able to consistency stay on the 5 GHz WiFi through the house, having to use the 2.4 GHz network with its better range most of the time. I've never been satisfied with "range extenders" because of the performance hit.
I came across
these simple directions, which happen to be for the exact router I already own but out of necessity was placed in a far corner of the basement rather than in an optimal location for even signal coverage. So I bought another of the same router used on eBay, and after configuring it, placed it in the opposite end of the house upstairs. Now I have rock-solid 5 GHz signal everywhere, and speeds equal to what I get on the hardwired network.
The first router is connected via ethernet to the second. SSIDs and passwords are duplicated on the second router so the handoff is seamless. The only thing different in the second router's settings are assigning a fixed IP and disabling DHCP. It actually took me longer to terminate two new cables than it did for the new router setup.
The only caveat is you have to have ethernet cable run from your existing router to the second one. I had the builder run Cat6 to every room so for me that was easy, but for older houses you may have to go fishing.
TL;DR: Don't buy a WiFi range extender. Get a second router and configure it as an access point.