How do I allow my den, with door/window cut outs that face into the dining room, to double as a spare room? ?

The den has a cut out door with p through windows on either side of it. I'd like to make the room double as a den/office/spare guest room and need ideas on how to enclose it in without actually closing the space in. I was considering a cafe door or informal french doors and plantation blinds for the window cut outs. Does this make sense for an interior room with no "true" windows? Any suggestions would be appreciated!