Any device that can give wifi to a switch?

So, bare with me here, it'll take a while to explain.

Illustrated: https://imgur.com/a/5BJtB9V

Skip Bolded if you've looked at the image

I've got a gigabit connection via a gigabit box. I've got a router plugged into that box and I've got a server plugged into LAN 1 on the router.

The router, server and gigabit box are all within a metre of each other. This is all on floor one.

I've then got a gigabit switch connected to port 2 on the router via a 20 metre CAT6 cable going to Floor 2. Connected to that switch on ports 2, 3 and 4, I have three other servers.

This is all fine and dandy but the users are complaining of slow Wifi speed even though it's on 2.4/5GHz (Can't have it on just 5 cause some of the devices aren't compatible).

I can't move server A to Floor 2 because the one user that uses it is Wheelchair bound. My users don't want to have to go downstairs for decent wifi. The wheelchair user doesn't use WiFI but if I swap around the position of the router and switch then every device suddenly can't access the Internet.

I could put the router on floor 2 and run the 20M cable directly from the box to the router and then have another cable running parallel to it back to Server A but that seems a bit inefficient.

So I figure the best thing to do is find some kind of dongle that can be plugged into a Switch to allow WiFi? Does any such device exist?