How techie are you? If the answer is not very much, then forget about this; but, if medium, then I would try to set up a custom domain so that all your emails are easy to migrate.
For example: you buy fosterj.me, and now, all your emails are like: hello@fosterj.me, service@fosterj.me, or even, lets say, university@fosterj.me
This way, you would only have a single migration to do (Gmail -> fosterj.com), and, from then on, you are independent to choose which provider to associate with.
For this providers, you have the following options (which, if not tech savvy, you can use without the custom domain, simply by registering, lets say, fosterj@icloud.com or fosterj@protonmail.com):
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Apple: Ok, they don't sell your data, but they CAN do it and they hace access to all your mails
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Protonmail or Tutanota: They DO NOT have access to your emails, only YOU can read them using their SEPARATE apps (so, no more apple mail app, but, in exchange, you are private from your provider)
I would personally recommend ProtonMail + Custom Domain, or simply ProtonMail, but it depends on what you can and w@nt to do :p
I hope I was clear, feel free to ask me for more clarifications!
Tagging @akalanka@masto.es for more context
Feel free to answer on this thread if you need more help!