listmonk is a replacement for Sendy. You can connect your SES account to it using the SES SMTP interface.
Integration with in-house DBs was a top reason for us.
Try to implement bounce processing soon - an average list decays at 2% per month (3% for B2B lists) so in a few months, the bounce rate can be high enough for mail box providers to start blocking your emails due to attempts to send to large number of invalid email addresses. Especially sensitive issue with your list size and sending volume.
There might be a couple more useful nuggets in this article on email deliverability best practices https://www.bigmailer.io/blog/improve-email-deliverability-b...