On many android phones there's a "do not disturb" option that can be configured to allow calls and messages from stared contacts and nothing else.

Does it also work selectively for e.g. Whatsapp messages?

Keep whatsapp notifications enabled, but then turn them off in the app's settings. Then, for the person(s) you care about, go to their chat and set up a custom notification.

Yeah, but if I use the "don't disturb" option of my phone, will it not mute all notifications from all apps (except phone and sms-messages)?

You can whitelist apps, too

I disabled all social media accounts and now only get notifications when people call or text me.

Incidentally, very few do (siblings, girlfriend, the occasional friend making an appointment).

If you’re on iOS you can configure specific ring tones & notification sounds for individual contacts. Look under settings.

- to be clear: I’ve found it very easy (no experience with android) to very strictly limit who I’m notified by and the personalized notifications really helped.