There are only 3 usable channels on 2.4ghz. If you have a bunch of houses around you, it’s quite possible they are using up 2.4ghz. You can find this out by using a WiFi stumbler or spectrum analyzer to see how busy those 3 channels are.
Your money would probably be better invested on upgrading problematic devices to 5 ghz.
It's dual band and has great coverage even with the location and radio turned down (in the basement of a 2 story). If you're having issues in 1200sqft, maybe it's a noise/traffic issue?
I’ve had very good experiences with TP-Link hardware reflashed with OpenWRT.
Before that, "the modem/router" was something I constantly had on my mind. No internet? Is it DSL or the modem? No network? Is the modem off? Should I reboot it? All these issues are gone.
OTOH, I live on a large parcel in the woods and can barely see any neighbor's wifi. I can use all 3 2.4 Ghz channels and the four outdoor rated 5 Ghz channels, with basically no interference, so it's wifi on easy mode.
The key thing is to run wireless routers in access point mode, and use something else (I prefer FreeBSD, but have used carrier modems when I was lazy) to do the routing, then you have separation of concerns. If you want to go crazy, I've actually got two FreeBSD routers with failover (CARP) and a custom PPPoE daemon to handoff the session with failover to LTE when the PPPoE session drops.
See the Reddit.