@lessthanmore Have you looked at something like this?
It’s a tiny dongle the size of the iPod Shuffle of old that can play Spotify and Amazon Music. Their spec says it should last up to 4-5 hours with Bluetooth, though in my experience it never lasted more than 2-3 hours. Still, enough for most long runs, not to mention regular runs.
Best of all – it works with any watch that you use