I recently wanted to share a grocery list/todo with my flatmates and I realised only I use Reminders.app which I switched to after Wunderlist news (though it's still kicking the last time I checked). Being on Mac everywhere and on iPhone since last 1.5 yrs migration was butter smooth.
I realise that I have been trying to de-googlify my online presence but at the same time I am completely inside Apple's walled garden and getting deeper everyday.
> someone that is "hard to deal with" for most people
This is what that has kept me on WhatsApp. I don't like Signal at all and Telegram is out of the question and no one else among I know is going to switch to Matrix.org/Riot let alone XMPP/Jabber.
> could spend time on going FOSS on my whole digital life
I moved to mailbox.org for personal email. I noticed they have https://mailbox.org/en/your-office/ too. So I guess I'll give it a try. You could try to find something similar. Private, open, at the same time you don't have to get your hands dirty at the lowest level.