Choose elements that switch-hit. Find a table that can function as both a desk and a dining table. Get daybeds or deep sofas that can double as guest beds. A storage ottoman can provide an extra perch, a little table, and a secret hiding place.
A new bed for David's room. He asked for a shelf above the bed as well to put books and a clamp reading light above the bed. Maybe extend the end of the bed for extra storage? Might make the bed a bit taller as well to make room for his Lego bins.
In a reach-in closet, KALLAX converts floor space (often cluttered) into organized storage for folded clothing or linens. Storage units easily become dressers for accessories and undergarments with the addition of optional drawers and bins.