What is the extender or other device which will insure reliability and consistent coverage.

I have a small home of less than 1800 sqft.   The WIFI coverage is crap.  I purchased from ATT less than a year ago a network extender.  The one recommended by ATT at the time was an AIR 4921.  I seemed to sort of work because it picked up my SONOS speakers.  I was still not happy with the coverage.  Noting that it no longer services any network devices I attempted to trouble shoot my network and found it was not compatible with the 2 Wire 5268AC provided by ATT.  So, I began looking for a new extender.  There are many on the market and once burnt twice shy I am looking for some kind of assurance of any ATT recommendation.   It seems perhaps replacing the 2Wire device would eliminate my coverage problems.  Is there a third-party product or service I could employ to solve my Delima?  I feel it is the provider in this case ATT who should fix the coverage.