I recently discovered https://supabase.io/ a neat PAAS which bills itself as an "Open Source Firebase Alternative."

It provides many features of Supabase like auth, realtime, and an easy REST API. It's built on postgres (which addresses many of your issues). Each API is open source and the whole thing has the option to self host.

They just entered beta, I've built a tiny project on it and had a great experience and plan to try it for my next, slightly-larger-and-might-want-to-scale project.