Suggestion : SportVitals app $6 bucks, seems pretty good!

I checked the app metrics, They are based on science and very similar to Garmin 
Explained on link- https://www.reddit.com/r/SportVitals/s/pXczYRsCa7

This set up work great with Apple watch and Fitbit Air.

SportVitals app: $6
Health Sync app: $4 ( I think)

Have apple on afib mode ( More hrv readings) 

Every Time you want to see metrics 

1. Open Google Health app let the data sync
2. Open health sync and sync data ( just have heart rate checked or data get messy in apple health)
3. Open SportVitals to see data and metrics 

JUST WANTED TO SHARE THE INFO AS A USER OF THE APP , IF VIOLATE ANY RULES YOU CAN TAKE DOWN.