There's a search engine called searchencrypt.com that claims to be more private than DDG. I took a look. I couldn't find an explanation of where their search results originate from, who they are, what their business model is, where their money comes from, or why they want us to install a browser extention that has access to all our data. I think it's possible to create a default search engine without installing an addon, and the only addon I've installed in Waterfox is PrivacyBadger.
I see from their "about page" only that the company operates out of Limassol, Cyprus and from their "terms of service" page that the software is copyrighted. Without more information, I don't think I will be using this one.
I've eventually chosen searx (about) as my default search engine for my Waterfox browser, using an instance of it hosted by Disroot.org. Steps to do this:
1. opened https://search.disroot.org/
2. clicked on the down arrow next to the search box.
3. chose the option to add SearX to the list of search engines.
4. clicked on "search preferences", (which takes us to the right place in Preferences.'
5. clicked on searx to make that the default search engine.
I also made searx my home page.