I did the free router upgrade last week. I rang up 2 degrees and said if I resigned for 12 months would I get a new router? They said yes and it's a Fritzbox 7590. 7590 has more wifi radios in it (4) so I can use it as the centre node of my mesh system. The good thing about fritzbox is the old router can now be a mesh point. Fritzbox is not wifi 6 it's worth noting but the price was right.
To get a decent signal to your TV I would use a powerline adaptor or put a mesh access point next to the tv and plug the tv into the eithernet on the mesh point. This way your TV is using the awesome wifi in the mesh point not whatever it got shipped with.
Plex is hard to get a reliable steam from in my experiance.
I only wish the new FritzBox had WiFi 6. These are one of the best modems out there. I needed the WiFi 6 standard due to me working from home. Otherwise i would have a FritzBox hands down.
The FritzBox UI is one of the most polished out there.