WiFi WTF

First off, thanks for reading. I’m feeling like a moron right now for not being able to figure this out on my own.

Problem: dead WiFi zones in our house, including 20 feet from our router. Cable internet, no cable TV.

We have:

- “up to 100 Mbps” service that speed-tests at 72 Mbps in rooms near the router and 20 Mbps far from router

- rented modem/router from ISP

- large house >5000 sqft across 3 floors

- 3 WiFi devices always on network (Nest thermostat, etc)

- 4 TVs. 2 are smart, 3 have Amazon firesticks (One of the smart TVs is too old to support Disney+ without one.)

- 2 laptops, no gaming PCs, up to 2 tablets, up to 4 smartphones

Questions:

- Can I add mesh routers to an existing router/modem combo, or do I also need to replace the existing router?

- Would mesh routers even be a good idea if the Amazon fire stick on the TV that’s 20 feet from the router can’t reliably get service, and we can’t reliably run a Zoom call anywhere in the house?

- Would replacing the modem/router be a better call? If so, what specs should I look for? I read that 2.4Hz is better for larger distance, and that it would limit me to N-type routers. It didn’t look like I’d be able to support very many devices.

Thanks again!