There is a save room directly opposite the boss room! They’re marked with a little save icon on the wall to show there’s one there!
Whoops! I feel a bit foolish as I actually found the save room in question, then forgot! Sorry about that. BTW, was there any specific tool used to create the GB-style graphics? I'm using Monochrome Spriter currently (Page), but am interested in learning about a variety of tools before I begin a project. Nice game:)