Exercise : design wise, what are the advantage and disadvantage of a physical button (e.g. screen tap or click) compare to the gaze you just saw before? Think about the device you have right now but also the wider spectrum of devices.
Example of room scale buttons using https://github.com/caseyyee/aframe-ui-widgets . Note that this only works on the HTC Vive or Oculus Rift, not a smartphone.
Consider also how this framework will work in a larger ecosystem. Check for example how you can prepare for upcoming Google DayDream thanks to a 2nd phone.