I like Fastmail but I'm starting to feel that the subscription cost is a bit overpriced for the way I use it (just IMAP email - not using the app, calendars, contacts, file hosting, ...). I've researched and found some other independent paid email providers that are significantly cheaper, although I suspect most of having a low bus factor with just 1 or 2 people operating them.
i have been using posteo.de for the last decade with no problems at all. Exactly the feature set you use. I only recently started to use their Caldav stuff which works.
I recommend them.
It's likely that regular Fastmail users are subsidising their AI costs. I've talked to several people who were a bit shocked when Fastmail decided to complicate their offering with the current hyped trash.