There’s no coupon code or referral, I’m suggesting these providers because they are the best, though if you wait until Black Friday there’s usually a discount for new account members.
Protonmail is a Swiss based email provider that promotes privacy and security as its business model. https://protonmail.com/pricing
Cheaper but equally as good so good it’s often debated which is better. Tutanota is a German based email provider https://tutamail.com/pricing
When signing up to either service I recommend making your username different to the email address you want to use and only use the username to login and contact support to avoid phishing attempts it will also give you freedom when choosing an alias as your primary email.
As soon as the DNS changes propagate, your setup will be complete. If your domain gets leaked simply delete and make a new one.
If your preferred alias isn’t available you can make one by using a domain name you can buy from a registrar like GoDaddy, Namecheap or Domain.com then apply some records to the DNS.
Applying DMARC to your email domain can help thwart phishing attacks.