I use a custom domain with iCloud+. That works for me because I'm very much in the Apple ecosystem, but I can easily move somewhere else whenever it's no longer the best option for me, and I did just that when I moved from Proton to iCloud. I've set this up for my wife as well. It can be as simple or as hard as you want it to be, but above all, I'd strongly encourage you to use a domain you own. Email has become our de facto identity, and we should be in control of it.
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