Cut out a piece of wood that's slightly wider than the bed frame and 24 inches tall. Attach it to the bed frame by drilling holes through the frame and into the footboard, then inserting 2-inch wood screws and tightening them with a drill.
You can use a door as a footboard, retaining the door's shape and look by cutting off the sides, top and bottom but keeping the center, particularly if it has inlays or decorative wood styling. Keep doorknobs and hinges attached to the door to accent the fact that it's a repurposed door.
Alternatively, lay multiple flat boards that are slightly longer than the width of the bed next to each other. Set two boards on top of them, perpendicular to the bottom boards, and attach these perpendicular boards to the longer boards with short wood screws. Attach the entire assembly to the bed frame.
Position a wooden bench with a high back against the bed frame and attach it to the frame with wood screws. Benches with no back can be used as well, provided they have solid rear boards for easy installation.
Set two vintage wood and glass windows against the frame of the bed and attach them to the frame by carefully drilling screws through the bed frame and into the window frames. Attach support boards to the windows if the window frames are too thin to easily support the attachment where it's needed. Attach the support boards across the joint between the windows and any other place necessary.