Extender to pair with WNR2000v3 router

We have a N300 Wireless Router/WNR2000v3. We've moved into a larger two-story house with some not quite dead zones, more like stagnant ponds. Also, our streaming device is struggling.

Which router extender would be a good fit?

I was looking at the AC1200/EX6200 and the N600. I figure I'd getter better advice here than at a big box store.

Also, how difficult are these to set up?

We're a Mac-based household and our streaming device is an Amazon Fire box.

Thanks in advance.