Instead of a wifi range extender I would get something similar to this:
https://www.amazon.com/D-Link-PowerL...70_&dpSrc=srch
You won't get nearly the advertised Mbps but it will be a way more reliable connection with lower latency. Just make sure to plug both devices, at your modem and xbox, directly into the wall. (don't use a power strip as it will degrade your signal)