I have found the built in sleep tracking of my samsung active 2 to be good. Maybe you could strap the watch to your ankle instead of your wrist?
Example: on Sunday, I woke up, drove 20 minutes to a trailhead, proceeded to strenuously hike for an hour, drove 20 minutes back. When I checked the sleep log later that day, the watch had automatically assumed I had been sleeping through the entire hike.
I like most other things about this watch, but sleep tracking is not one of them.
But the sleep tracking has been awful. A lot of days I'll get up, sit in a chair, and will surf the web for several minutes, say 45 minutes, and the watch inevitably records this time as also sleep. It's quite ridiculous and the software doesn't allow you to edit the log with the correct time. You can only delete entries, not edit them.