Typically MailProvider would let you have <yourusername>@mailprovider.tld and sometimes a limited amount of aliases, right? With some you can bring your own domain and have <yourusername>@<yourdomain> most of the time also with a limited amount of aliases.

Migadu let's you pay a flat fee, bring as many domains as you like and use unlimited aliases. Their pricing scales with actual traffic, not arbitrary limitations on your address namespace.