Google Chromecast is likely the best and cheapest option for mirroring your Ubuntu desktop to your TV. Here is a short youtube video.
For setting up in Ubuntu 16.04 there are other users to help out if you have a problem: Google cast on Ubuntu 16.04
Note there is a now a version 2, an ultra option and even an Ethernet option.
The cost (without options) is reasonable around $35 USD.
Although this is the recommended option for the OP, check your TV model first before buying a Google Chromecast. It could very well be your TV already has it built in. Also check your blu-ray player as some of them have Google Chromecast already built in too.
Google cast extension has been discontinued, now is integrated into Chrome/Chromium: