Let me take this chance to mention the "Unhook" Youtube browser extension, which I recently added and which I think has been having a big positive effect for me. The extension allows you to remove (among other things, it's very customizable) the sidebar of suggested videos from Youtube.

This extension has been more effective for me than any other at cutting down how much youtube I watch. Maybe the biggest factor in this is that it doesn't ban me from youtube entirely - When I've tried extensions like that in the past, I've always ended up uninstalling the extension when I needed to watch a youtube video for work. This way, I can watch a little, but the lack of constant new recommendations keeps me from spending hours and hours on the site.