https://litestream.io/ does streaming replication to S3 (or similar service). With this, you probably have better data durability than a small database cluster.
Instance can be process, container or machine.
If your db does lots of work, I buy new ones, install them in the datacenter, bring them up from backup.
BTW: you skipped a step for a busy database: warming it up with shadow traffic.
Under certain scale just switching like you describe will cause just as much downtime.