There are free services that allow you to create countless emails, one per site is ideal, just like one (different) password per site. Addy and Simplelogin have a generous free tier, last I checked the first one allows for unlimited receive-only addresses (when shopping it’s very rare you need to respond), the second gives you some two-way addresses.
If you get a domain, many registrars include free mail service, and have mail forwarding, or “redirecting”, which basically will allow you to create countless addresses (that can also send/respond) for your one account (You add these “email forwards”, or “Identities”, to your app of choice, like K9-Mail for android). You don’t necessarily need to buy their separate email package (although the interface might be more convenient). I’ll give you one example which includes email: OVHcloud, one of the largest clouds in europe.
If you can afford it there are all-in-one services like Soverin with easier interface.
It might be wise to start a slow process of migrating (or maybe deleting and creating again) accounts, and saving all this stuff in a password manager (like KeepassXC) if you aren’t already.