You don't even need to provide your own domain - Fastmail gives you a subdomain for free. For example, if your Fastmail address is myname@fastmail.com, then any_address@myname.fastmail.com will get to you.
Does this really need to be said in 2022? The advent of plus addressing was more or less driven because techies were already able to make custom addresses for their domain, and the + could be a standard thing that non-techies could use with their basic email account without needing to reconfigure things on the backend, or use a messy catch-all account.
