For whatever reason, if you’re like me, and you discover that the Move to iOS app does not fully move your SMSes (don’t ask why!) – there’s a backup.
You can use mDroid SMS Backup & Restore (not the Carbonite one) to export messages to CSV, and then upload them to google drive. You can export into text and email to yourself as well. The latter is preferred since you can always access it via gmail!