I pre-ordered a Pebble Watch.
I do love the fact that it can last an entire month, have the bare minimum, relaxing E-ink screen and is embraced by an apparently lovely community passionate about FOSS.
Also fully compatible with Gadgetbridge from day one. 
The CEO also looks kind and apparently cares about real things (no AI salesman or whatever).
It might flop. Will not be as refined as an Apple Watch Ultra but hey, I do value some points over others more. Would be a perfect match for GOS and some basic healthy metrics IMO. 
PS: you can hack the hell out of it and have something playful and fun.
Gosh that one is a thing most company are loosing nowadays.
Besides that, Garmin maybe? Their support on Gadgetbridge looks subpar and their software as a whole is not the best from what I saw. But, it’s some kind of well known brand if you also need to have something a bit more rugged. 
PS2: Pine or Bangle also look like decent solutions.