I bought a domain name and set it up on tuta to get an email address that I like. It was super easy to setup, tuta had created a video tutorial that showed how to setup a custom domain step by step.

I did the same thing, switched to tuta and bought my own domain. They had but together a video tutorial on how to fill out the needed values to use the custom domain. It was super easy and I am very happy with this new setup.