If all you need is to have your own email addresses on your own domain without paying anything look into Cloudflare free tier they offer MX routing that can end up on your existing Gmail email (or any other mailbox you own anywhere) so long as the domain DNS servers are managed by Cloudflare. It’s completely transparent to the end user.
From my experience the only drawbacks are if the email volume increases they might ask you to pay and you don’t have much control over which emails get rejected due to sender reputation. If they decide to dump an email, it’s gone and you can’t get it back in any way.