Pull out Wardrobe Rail for under stairs. You could have a few of these attached under the higher stairs and some storage boxes or even a chest of drawers underneath, then you could do away with the black frame and the room would look / be much larger.
Drawer runners & Drawer slides - Pull Out Wardrobe Storage
Yes! The cupboard under the stairs is ridiculously awkward and completely useless when it comes to storing anything other than the Hoover. No more crawling into the back of the cupboard to find things!