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.