Honestly, Azure DevOps is a solid replacement. The integration is really good and the "Boards" software really feels like they're eating their own dog food. Their Wiki software is Markdown stored in a Git repo (unlike Confluence's mess). It's fast, permissions are relatively intuitive and fast, etc.

It's worth a look if you're evaluating.

JetBrains Space is another alternative, but I have no experience with it.

Treat it like a software problem, start with the simplest thing that'll work and then introduce more complexity or features when you need them. Chances are you'll start with GH issues or a shared doc in a productivity suite and where ever you land, it won't be JIRA.

Confluence search has a lot of issues. Its almost impossible to search for documentation or anything there. Even Slack search is leagues better and can be used as a documentation/ help tool.

README.md

Trello was good, although it's quickly being run into the ground.

Mediawiki is a pain to maintain but nothing else comes close.