[Closed] Which Forum? ...seeking advice on a forum(!)

Calling lovely friendly IT people...

I wonder whether anyone might be able to advise at all on a suitable online forum to use that they have experience of?

- It's for a non-profit network involving refugee resettlement
- It needs to be private/secure/closed as some discussion topics are sensitive
- I need to be able to embed it on a Squarespace website
- It needs to be relatively cheap, as the group is relatively small, with a limited budget

So far looked at:
- Muut - but you need a medium sub to be secure $96/month (expensive)
- Website toolbox - but not enough info about creating secure site
- Forums.net - starts at $49.99 (still pretty expensive and limited design options etc)

Thanks in advance

Kind regards, John