I am moving apartments next month and there is new internet situation for me in the new apartment. The fiber wall socket which has always been somewhere in the living-room in all my previous apartments, is now in a closet right by the entrance, in the same closet the electrical fuse box is. It is clear to me that I will have to put my sunrise box router there, and then pass the connection through the in-wall cables (already installed) to the rest of the apartment.
Now the thing is that despite having a LAN socket on every room, I will still need a good wifi signal for other reasons (mobile phone, smart home devices etc), and obviously, the wifi signal from the router inside the closet, will not be ideal. I am not sure what kind of device I need to connect to the LAN socket in the living room, in order to create a wifi network from it? Would that be an access point? Or are there WIFI extenders who can have LAN internet signal as input?
As others mentioned already: You might need so-called Wireless Access Point, this is a device that's completely independent from WiFi built into your router and acts as a bridge between wired connection to router and your WiFi Devices. I guess it is in some way exactly what you meant "a mesh extender of WiFi over Copper cable".
There is gazzilion of products for this, most user friendly during setup are probably Ubnt devices but if you have a IT savvy friend then I would strongly suggest a Ruckus Unleashed device such as R610 or R710.
This is enterprise grade hardware with very cool standalone firmware (no cloud crap) from original manufacturer that allows their usage outside of enterprise. You can buy them on eBay and they cost several hundreds but one such AP is able to cover much greater space then several consumer grade devices
The apartment is not very big, it is a 2 room apartment, around 70 square meters but the layout is tricky, as said closet where the main connections hub is located, is not in direct contact with most of the apartment. Especially between the router and the bedroom, there will be like 3-4 walls plus the closet door.
The double-NAT is a good idea, I will try it first and if I don't have any issues with communication between devices (got a lot of smart stuff), I will keep it. Otherwise, I will opt for an access point as suggested.
I would wait until you move into the appartment and see how the wifi works. You may end up being pleasantly surprized. If not it's no big deal to get an access point (AP). You just plug it into one of the wired plugs. They're easy to set up unless you're trying to do something fancy. Do change the default password on the access point.