So the big question is how much content is in these subfolders?

The simplest solution would be to use categories. Your category would replace your subfolder and then each post would be the content/page name.

Alternatively you could use something such as a 301/302 redirect to redirect traffic from your old content page URL to the new one, so you won’t lose any traffic and eventually with a 301 permanent redirect your google indexes will update.

I’ll have a look at the categories side of things.