The keys have been found! There is a little shelf unit by the door that holds the record bowl tray where keys go, and apparently, they escaped over the edge and onto the floor. This morning, when grabbing the keys I've been using, something else flipped over the edge, and when I pulled back the shelf to pick it up, there were my keys! (amongst a pair of shoes and a lot of dust balls) I didn't figure out what it was the actually fell, but I'll deal with that tonight. =)
I'll figure out who had the suggestion (here and/or on Ravelry) that would have led to this location, if I wasn't just generally clumsy in the morning, to arrange the yarn. Thanks for all your help!