Sorry if this isn’t what you are looking for, but I cannot fathom any reason to recommend free web hosting. It may be free to you, but it imposes costs, in perhaps nothing more than dealing with pop-ads, on your users/viewers. I can’t think of any pros.
With the free hosting, you can’t use your own domain name. Perhaps someone can host it on their personal page that comes with most any Internet access account these days.
I would hope your not-for-profit could, if necessary, spring for the $10 a month or so it takes to get a paid website. Even if you have to try to raise funds simply to pay for it.
But I really wanted to share one other recommendation. Try to identify a mid-size company and ask them to host your website as a community service.
In two different technology companies I worked for, we had a few not-for-profit websites we hosted on a server at no cost. If you can find a company whose interest fit hosting this particular not-for-profit cause, all the better.