I'm still getting by with my Pebble Time Steel, and I've been watching (no pun intended) Fitbit's releases to see if they're yet up to snuff. It looks like the most recent revision of their smartwatches would work OK for me (and add HR sensor). Don't know if they'll be sufficiently reliable, since this has been a weak spot for Fitbit in years past.
If I'm able to eke out another 2-3 years, I might get an Apple Watch, which would presumably have 3-4 day battery life by then.
I tried the charge3 and the step and stairs-climbed counters both read wildly incorrectly. It also had a tendency to track steps taken when driving. They also hadn't got the pulse-ox sensor doing anything at the time I returned it.
The OS on it is quite nice, the iOS app isn't bad either, but the inaccuracy just drove me nuts.
I moved on to a Garmin vivosmart instead. Not quite as pretty, but a lot more accurate.
If I'm able to eke out another 2-3 years, I might get an Apple Watch, which would presumably have 3-4 day battery life by then.