I have two domain names. One goes to anonaddy and I use that for all non-important stuff. Maillinglists (for discount), orders on a sketchy site, signingup for social media.
The other ends up at protonmail and is for more serious stuff I don’t want to route via anonaddy (while I trust the developer and the service, I just want extra safety). I use aliases at protonmail as well to know where stuff comes from.

Deciding which domain to use depends on a couple of things:

• what happens if they access my mail. Is there a payment option connected, can they get into other services or request stuff from the government? If yes, chances are I go with the proton route.
• do I expect a lot of advertisement, selling of my data or security breaches? If yes, I go with the anonaddy route.

For amazon I use the anonaddy route. I do not add my creditcard or bank account to my account and if they do gain access, they will only get my email.

Hope this helps.