Include a soft rug or carpeting where the textures and surfaces are comforting and good for curling up with a book or puzzle or simply playing on the floor. Consider adding some big throw pillows near the bookcase [if you have one].
Made to measure vs Built In. Look how much nicer a separate wardrobe looks in this nook than a wall to wall built in unit. Just measure up and have the unit made iso commissioning built-in mommo design: A VINTAGE TOUCH - WARDROBE