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.
Attic Bedroom Closet Design, Pictures, Remodel, Decor and Ideas - page 9 - sublime-decor. I have the perfect wall (with attic behind it) to do this. I've often thought of making an easily accessible closet there.