How can I have 2 mailboxes for 1 user?

I signed up for paid business email. I am the only user at this time.

I would like to have a personal mailbox and a business mailbox under the same user (myself).

If I understand correctly, alias email addresses will all go to the same mailbox and will not be separate.

I tried to add myself as 2 users but it won't let me add myself twice.

Is it possible for 1 user to have 2 mailboxes? Thanks