+1 to running. If you run consistently, you'll learn to believe in your body as something that naturally improves if you train it well, and that belief will cross over to your mind and heart.
+1, had the fortune to work with him at a previous startup and meetup in person. Our convo very much broadened my perspective on engineering as a career and a craft, always excited to see what he's working on. Good luck Simon!
Had this exact problem (Heroku Postgres to RDS) at my old co. Data migration went as bad as it possibly could (dropped indices, foreign keys, everything but the data itself). This would have saved us months of pain.