Looking for Wearable advice - accurate, long battery life, no extra apps

I’ve been using Sleep for a few years now. My first wearable was a Mi Band 2, whose accuracy I was fairly happy with.

Ultimately I gave that one away and picked up a Mi Band 3, as an affordable device that didn’t require server-side authentication.

I was never very satisfied with the Mi Band 3 as it seemed less accurate than its predecessor for me.

For a time I only used Sonar. Despite much fiddling with the settings, I could never get it to be accurate enough for my liking, especially for awake detection.

Additionally, Sonar used too much battery for my tastes.

I am looking to get a new wearable, then. These would be my wants:

  • its main function will be to track sleep, so everything else takes a far backseat
  • long battery life
  • good accuracy
  • batching, so to save the phone’s battery
  • native Sleep support so I don’t have to install anything else

I realize this will exclude most cheap bands, and probably Wear OS devices too, unless there’s one which works with MicroG?

Can you please advise on my options?