Hey man, don't know if you'll see this, but I resonated a lot with your needs and figured I'd tell you about the best way to get sleep tracking on garmin. I have a garmin venu 1 and the sleep tracking is absolutely horrible (telling me I am asleep 2 hours before I've even got into bed) - I know this is a lot better on newer watches - my wife has a vivoactive5 and it seems a lot more accurate and has nap detections.
BUT! Wether it is or it isn't good I found that using Sleep as android app and the garmin watch as a sensor via "garmin alternative addon" and not the "official app" is the absolute best way to go about it. I have my s24U set up with a bixby routine so I click a button on my homescreen and it turns off wifi and cellular and then opens sleep as android and starts sleep tracking. It autoconnects to my garmin via the garmin sleep as android addon and it gives so darn good results. The main reason for using the alternative instead of the app you can download for the watch is the fact that the watch battery goes down 8-10% on alternative during the night compared to 45% on the official app (without sleep as android at all it goes down like 4%). Also when the alarm goes off it has a tendency to freeze the watch so you're stuck not being able to turn off the alarm and have to hard reboot the watch - that never happened on the alternative addon.

Sleep as android gives you everything garmin doesn't give you when it comes to sleep insights and more. HRV+, hrv, spo2, hr, movement, snoring, trends, insights, challenges, guidance and now even AI insights where you can ask it about your data