Cooking the RDS equivalent is reasonable amount of work, and pretty big amount of knowledge (easy to make failover solution have lower uptime than "just a single VM" if you don't get everything right)

... but you can do a lot with just "a single VM and robust backup". PostgreSQL restore is pretty fast, and if you automated deployment you can start with it in minutes, so if your service can survive 30 minutes of downtime once every 3 years while the DB reloads, "downgrading" to "a single cloud VM" or "a single VM on your own hardware" might not be a big deal.