Try one of those booster antennas like the one above.
There are WiFi boosters, which are effectively a "WiFi relay" - they work OK, but usually only with kit of the same manufacture. I've heard of many folks with one of a different brand tearing their hair out...
My inclination, if you can do it and if the base unit has a spare socket, would be to run a Cat 5 cable towards where you sit, and stick a second WiFi unit on the end of that.