After reviewing this thread, iCloud+ is top of my list for migration, and I don't even own an Apple-anything. (Migadu is my secondary choice if this iCloud+ thing falls through for some reason.)

From what I've been reading iCloud+ has some limitations, but it will fit my needs. An iCloud+ subscription costs $1 a month ($1.29 CAD), and the subscription can be shared with a "family" of up to 5 other iCloud accounts. iCloud+ supports up to 5 domains and three email addresses per domain per person. Domains can be shared between the family or not. I also trust Apple to have a competent security team.

I'll probably start the process this month.