Getting familiar with Outlook's keyboard shortcuts might be the ticket:


Search All Mailboxes: Ctrl + Alt + A
Search Current Folder: Ctrl + Alt + K
Include Subfolders Within the Current Folder: Ctrl + Alt + Z


Since you've set the default search to All Mailboxes -- which can be done by pressing Ctrl + E -- press Ctrl + Alt + K for those times you want to search only the current folder.



This method is compatible with search filters, e.g., from:XYZ, hasattachment:yes OR no, etc.