I have been using a BangleJS 2 for the last year, and have quite liked it. There is a companion app, Gadgetbridge, to install on your phone, which is available through F-Droid (there is a Bangle-specific version of it, or a generic version that supports a bunch of other smart watches). There is also an app store (all free software) for apps that run on the Bangle itself. It includes a heart monitor, but no music streaming.
I've also been watching rePebble as they start making new Pebble smartwatches. I've never owned one, but a lot of people swear by them. They are now fully open source and have an app store. No idea if they can stream music.