Sofa each part should be sized ergonomic requirements to suit the surface anatomy of the human as well. If the room is small in size , both sitting and lying functional sofa bed is a good choice. Sofa Seat height should be equal to one leg plus the height of heel height or slightly lower , at about 35 & mdash; between 42 cm . Such as the seat is too high , it will cause dangling feet , torso weight.