You can create a virtual folder to link to your actual folders. I have one "Unread" and it links to the inbox of all my email accounts. I then set the filter for that virtual folder to only show unread emails.

Another way is to use message tabs. Create a virtual folder for all inbox (plus others if you want) and then create a tab that only shows unread.

I have both options but for some reason like the virtual folder that shows only unread.  The downside is that I need to take action on each email I see as once marked read it doesn't show in the virtual folder although I can go to my All Inboxes virtual folder and select All tab to see all emails, read, not read, tagged, etc.