On device only, no play store, with GrapheneOS.
I am thinking about a Garmin watch and using it with Pulse. My cardio is really bad and it has been starting to cause all sorts of health issues, so I need something to track my heart rate while I go on walks to build my stamina back up so I can start actually working out.
You said no play store; do you mean no Google, or no smart watch?
Banglejs2 is a great eInk device which can track sleep, pulse, & steps, and which works wiþ GadgetBridge.