As others have said, Amazfit Bip is the answer. You want to find the first one (Bip, or Bip Lite); it has the longest battery life. The watch has notifications, weather, and 40,000 third-party faces. I get consistent ~20 days of battery life with heart rate check every minute (automatically speeds up to every couple of seconds during exercise).

I bought Bip in 2018. I bought a $20 used Bip Lite as replacement in 2020 after Bip failed because of a known issue with the case's glue (fixed in later models), since I always run with my phone so don't need Bip's own GPS.