The lightest and smallest GoPro camera (as of today) is the new GoPro Hero 4 Session. There is no screen for information or video viewing. You can always use your smartphone with WiFi connection for more controls and video viewing. The buttons are even simpler now with one-button control for starting recording. The old style GoPro mounts will still work with the Hero4 Session Camera.
The best part, other than the smaller size, is that that users won’t need a waterproof case. This means you will get better audio above and below the water. It is waterproof down to 33-feet, and can shoot video in 1440p x 30, 1080p x 60, or 720p x 100. Yours for $400.