Abstract: A sofa bed assembly comprises a carcass having an inside, outside and interstitial interface. Mechanical moving parts comprise a bed base mount assembly and gas strut all outside the carcass and interface mounted. A base supports a mattress held by base sidewalls, vertical within and filling the carcass with the sofa bed closed. An armrest supports a sitter's arm in the closed assembly and as is a proximal bed support in the open assembly. Pivoted leg supports at the end of the bed base rotate as distal bed supports. Alternatively, a sofa is moved to the end of the bed base as distal bed support. An armrest extension extends the armrest for the closed assembly and folds through 90° for the open assembly allowing the armrest to act as the proximal bed support. Armrest shields cover mechanical moving parts.