[Resolved] Custom 404 – easiest way to implement?

Hi! I just realized that the Ultra 404 page lists posts and categories, which I don’t want it to do. The grid plugin I use is pulling images from special posts that I make just for images, and those posts are being listed on the 404 page…want to eliminate the lists of posts and categories, and just leave the search box.

I’m pretty sure I could edit the 404 template to make it look like I want, but then I can’t update the theme without losing my edits.

What’s the easiest way to get around this? I was thinking that a child theme would be easiest, but I’ve already made a bunch of changes (via the customizer) and am worried about losing everything and having to start from scratch.

Have you got any suggestions about the simplest way to go about this?

Thanks in advance,
Lori