datendefekt

Yeah, what OPs asking for describes Nextcloud pretty well. There are good prices for managed hosting.

Polar is legit, and another really good (and super expensive) Finnish brand is Suunto. But you might want to steer away from XCoast. The prices are too good to be true, my first impression was that they might rebrand Chinese watches. And looking into the android store for their app proves me right

Would be nice if it could be self-hosted, but it looks like no go.