For a same issue. Like holidays folder, boys folders... Etc. Because all images in uploads folder, cause many problems in memory
This should do the trick https://wordpress.org/plugins/media-file-manager-advanced/ There is also a plugin here for that under the code examples http://4rapiddev.com/internet/manage-or-organize-wordpress-media-library-structure-in-categories/ Nigel
Actually, check this one https://wordpress.org/plugins/enhanced-media-library/ link 2 from my last post is quite old. This one will do it for certain and is current.
Unfortunately, when I add another subfolder, like Uploads/cars At this time, My old photos on other folders like Uploads/dogs Aren't showing.
What you need to accomplish appears to be doable you just have to keep looking at the plugin. You may need to rename a few folders and create them again from the admin, then simply move a few things around. Easy stuff really. N.