Do you have any Ethernet wiring in the house? Then I'd get an ubiquiti. Slightly technical though.
If not consider a mesh network.... You can add devices and they seamlessly work as one. More expensive than just adding a repeater but having multiple routers and networks in a house is annoying.
So, you're suggesting to dump the year old Asus I have a get myself a mesh router as opposed to just adding an Access Point for the existing Asus?
Railton
It may be more than one mesh router depending on the size of your house. I do understand there's more expense involved.
You can for sure just add a repeater; it does the job BUT you'll have your devices either hunting/switching between networks a lot, or have two different SSIDs so some devices use the router, and the others use the repeater. In my parents' house we have 3-4 wireless networks; Sometimes based on performance you end up switching networks, but you have to do so manually. A mesh network does this automatically and the devices communicate.
If you want it exclusively for the tv some repeaters have an ethernet port and you could plug your tv into that.
Just throwing out the option because they're quite a bit more sophisticated (and user friendly) than the traditional repeater option.
Another option would be to buy a mesh router and keep the ASUS and down the road replace it with another mesh router. Then use the Asus device as a repeater.