Create this beautiful built-in architectural feature by constructing an independent stud wall frame that extends two feet out from your secondary bedroom wall, creating a large rectangular recess centered around a standard twin mattress size. Face the new structural framework completely with smooth drywall sheets, cutting clean vertical lines to form the opening of your cozy sleeping pocket. Apply flexible corner beads, smooth joint compound, and fine sandpaper over the seams before painting the interior a soft matte forest green or navy blue finish. Build a robust interior wooden slatted mattress support frame inside the hollow opening, securing it tightly to the internal studs with heavy wood screws. Slide the twin mattress directly into the custom pocket, framing the opening with soft cotton curtains to complete the sanctuary.