This is a perfect combo of my two favorite ideas for that space under the stairs leading to the basement. A reading nook AND book storage and shelves . assuming that there is enough space for this there.
This ikea hack would be a great room divide. seating on one side into the kitchen nook & and additional bookshelf on the backside for storage. 10 Totally Ingenious, Ridiculously Stylish IKEA Hacks // Live Simply by Annie