The TV is on a secure WI-FI network which none of the users will have access to; therefore, I would imagine this would require an enclosed unit, such as the Amazon Fire or Roku. does any one know which may be best for security and ease of use?
Not all streaming devices support all streaming services so that's the first thing you need to make sure of.
An android box is the most flexible but would require more set up than a Roku, Firestick, or Apple TV.
If your office has a hardware firewall you may need to open a port and give permission for the device to access the internet.