You can use a custom domain using a personal gmail account if you forward email to the gmail account from the registrar and then setup send mail as using gmail.
If you're using Gandi (a registrar I would strongly recommend), you can set this up from your Gandi domain dashboard: Click "Manage mailboxes" and create a forwarding address. Example: https://i.imgur.com/qRmho7J.png - The MX values for your domain need to be Gandi's default email servers.
