I had your exact same problem in my old brick house that is hard to cable and not so great for wifi range. More powerful wifi wont add much as the wifi power is all limited to what the connecting device can also send back, and that wont change. You need to re-shape the wifi coverage of your home.
I run a second router configured as a dumb access point that shares the same SSID, and the connection between runs over a powerline type extender. You device will shoose the best signal to attched to automatically. Another option is mesh networking products.
google dumb access point to get started..