bed, couch, bench, chassis
牀 centers on a piece of furniture for resting or supporting something: a bed, couch, bench, or a structural chassis.
牀 combines 爿 (a bed or board) with 木 (tree/wood), suggesting a wooden bed or couch. The exact historical development is uncertain, but the component relationship is plausible.
The left side 爿 looks like a bed frame, and the right side 木 is wood. Picture a wooden bed or bench made from a tree.
For ショウ, imagine a showroom bed: a fancy wooden couch displayed under a spotlight. Show -> ショウ, and the bed is the star of the show.