I have the same issue. I want something simple but has encryption, native mobile apps for both Android and iOS, and threading. Facebook style posts with comments would be great.
For now we're using matrix and element bc I can find anything better. Unless something more compelling comes along we'll probably migrate to something xmpp based like snikket.
I'm not sure about libre office, but Excel has lookup and lookup. I've not personally used those. But might be of help.