@User42 Also, it's for a 3-story house, about1800sqft., with both back and front yards.

  @User42 

Quite a bit more information will be required to give you any actionable suggestions.

Which floor is the ISP Modem located?  

Is the ISP connecting via cable, fiber, copper DSL? I don't mean to sound ignorant, but Xfinity is not in my area, so I have no idea how they connect.

You say you want to replace the Xfinity router, is that a separate physical box from the Modem? If so then what is the manufacturer and model of the Modem.

What specifically is the Xfinity model number? 

How are networked devices currently connected (Ethernet vs Wi-Fi) and where are they located in the home?

What is age of your home?  Ask due to the differences in interior wall construction techniques over the decades. Concrete, Lath&Plaster, Dry Wall; all have different characteristics in allowing Wi-Fi signals to penetrate.

This is a good starting point. 

  @DAServices 

Thank you for your time on this. Best I can do in responding right now to your questions:

The ISP modem is in the basement. The ISP connects via cable.

The Xfinity router is a separate physical box from the modem. It is a router manufactured in 2017.

Networked devices are connected via Wifi. They are in the basement and the second floor. The Xfinity router is on the 3rd floor.

The home was built in 2004 and is mostly drywall. 

The Xfinity router works well to reach all devices (for the most part, 7 devices) throughout the house, but does not extend very far at all to the outdoors. I mostly want to get rid of the monthly rental fee I'm being charged, and potentially also get a router that extends further to the outdoors.

Hope this helps! Thanks again.

  @User42 

Sounds like replacing the leased router with a Deco would solve any number of your issues. 

You can expand the Deco mesh with up to 10 deco nodes. 

You may find that a 3node Deco M5 setup will be entry level for you but still give you the benefit of built in Antivirus and parental control. 

You can add more M5 nodes and or M3W nodes to the initial M5. 

Newer Models "X" have more bandwidth options and faster Wi-Fi Speeds.  But you may find all of the newer Deco devices overkill if your ISP is only 100 or 200MBps.