Will Additional Pods Help?

Long story short, I upgraded my internet service from the 300 Mbps service to Giga service. The actual speeds I’m getting are one issue but my real problem is coverage, which is next to nothing once I leave the room where my router was installed (by Cox, originally). 

Previously, with my 300 service the coverage was pretty good, and I also utilized a hard wired extender in the basement where my office is located, and my work machines all got a great signal and great speeds. 

Now, beyond the room where the router is located the speeds are either (really) 18-90 Mbps or in the basement either no coverage or intermittent connection and speeds which are completely unusable for what I do, let alone any “normal” browsing and streaming. 

Cox sold me a WiFi “Pod” device for $120 which is supposed to replace my extender.  This thing seemingly does nothing to help, and the only place where I can get it to actually connect and be online is in the living room where the router is.  Hence I can see why it does nothing  but it won’t go online anywhere else.  Before I go ahead and buy more of these infernal pod things, will that help?  If I say get two more and put one in our kitchen and another on the basement will they connect in a line and help with coverage?  

Or even better, can I buy an extender of some sort and simply plug it into the existing coax cable which is already installed in my basement where my old extender was?  I understand the one I had, which was rented from Cox will not work with the Giga service but maybe another kind will? Or are these pods the only solution ?  

My house is NOT huge, so these coverage issues are puzzling