The MTB pros and YouTubers are typically using chest mounts, chin mounts on their full-face helmets, or even normal helmet mounts. Maybe a chest mount is the answer for you? The GoPro Chesty is meh. I'd recommend the Stuntman chest mount.

EDIT: For ease of use and reduced complexity, maybe consider a simple helmet mount. Personally, I think chest mounts provide a more immersive angle (since your handle bars can be seen in the frame). Your call!