I want to use my main mail address everywhere, even public places.
No you don’t. It’s not quite as simple, but buy your own domain, get an email provider such as Fastmail that will let you use a catch-all, then use a unique address for every site you visit.
Then if one starts receiving spam, you can block that specific address and voila, no more spam. Plus you know what sites have either poor customer detail hygiene or are actively selling your details.