Ask HN: HA Database for the Single Person Startup?

I'm about to go down the road of a single person startup. Critical to the application is a database, that will be hosted on the cloud somewhere. Also critical, is getting sleep at night. What are my options for database high availability that are reasonably easy to manage?

I come from a background in PostgreSQL, and my problem domain maps well to a relational database. But I've done enough with Cassandra, and Elastic Search that I could make it work there as well, and get multi-node redundancy easier, but at the price of not having a relational database.

Of course, Amazon's RDS looks interesting as well, taking management of the database redundancy mostly out of my hand, but it looks like that could get expensive quick.

Any thoughts?