Help automating email sending process

Every day I need to send transactional emails. Not like order confirmations, these are gift vouchers. This means that a template can be used but part of the message is a unique code and/or an email attachment. The way I've been doing this is with a mail merge tool for Google Workspace called YAMM which works ok but is not ideal. Instead of sending through my Google Workspace email account I want to send from a Google Sheet through Mailgun, using Pipedream to connect the two. Or if there's a better way I am open to suggestions. I send an average of 50 messages per day but that number tends to increase. I probably have more tasks when this one is completed successfully.

Describe your recent experience with similar projects.