Expanding Across Building Floors

So as the title suggests our company will be expanding from the first floor to the second floor.

Right now I have 2 WAN connections that are load balanced / failover that comes with the router on floor one.

I guess my predicament is that both floors will be sharing this same network connection. What use would fiber be in this instance? Should I run fiber between the two floors to connect a switch on the second floor to the router on the first floor? Or should I just run Cat6?

There isn't a ton of heavy lifting in terms of network utilization -- mostly sales and some times some files syncing across the cloud and maybe some large files here and there from marketing, so I don't think it needs fiber. There is also no on-prem storage or VM infrastructure that would require such low latency or speeds.

Am I correct in thinking fiber wouldn't be necessary?