Don't pay hundreds elsewhere. For $118 here you get BOTH pieces of a split queen foundation style box set. Each measures approximately 30 x 80 inches. These will fit up or down that tight stairway.
As an added benefit each piece is fully framed so they are sturdier than a one piece queen foundation.
Please mention this posting to receive the promotional price of $98 for the set. Tracking the promotions helps us keep track of where it is useful to advertise.