The Mechanism Tradeoff
The pull-out or fold-down mechanism in a sofa bed requires the base to be relatively flat and rigid to form a sleeping platform. This rigidity directly compromises seating depth and foam density — you cannot have deep, springy sofa seating on the same base that needs to extend flat for sleeping. Premium sofa beds use an independent sleeping platform that drops below the seating level, effectively separating the two functions. This is the engineering reason quality sofa beds cost ₹2–4 lakh — the mechanism itself is expensive.