connectivity using Nighthawk AC1900 router with an EX7000 mesh extender

I'm at my wits end and thought I'd ask for some help, since Xfinity won't be of much use since I'm not using their equipment. So here's the rundown:

I'm using a Netgear Nighthawk AC1900 cable modem router, with a Netgear EX7000 mesh range extender. My apartment is kind of long/narrow, with the router on one side of the apartment in the bedroom (that appears to be the only cable outlet as far as we can tell), with the extender in the kitchen, halfway to the other side of the apt (which is where the living room TV is). There's a clear line of sight between the router and extender, though the 5GH band is about 55% strength getting there.

I've tried many different setups with this combo, and I still run into issues, which generally causes me to unplug the router or the extender or both.

Previously, we had it set to run with one SSID being broadcast from both devices, on both 2.4 and 5ghz. And there seemed to be no rhyme or reason as to when devices would get disconnected. Part of me thought that maybe my phone would disconnect when it moved out of range of the router and would try to connect to the extender, but the connectivity issues are happening more with laptops and TVs that don't tend to move much. After not having much luck with this setting, I noticed this Fastlane feature, which I've tried as well, but it's not much better. 

One thing I've noticed on occasion is after resetting the router or extender, I'll log into the router and it'll say that there are dozens and sometimes over 100 connected devices, though at most we'd only have a 2 phones, 2 laptops, 2 TVs, an iPad, a Switch, and some Sonos speakers.

Ideally I'd like to have one wifi name, and be able to move freely throughout the apartment, but I'm curious what others have done in this instance. I'm willing to try anything at this point.