Is a couple allowed to sit on the same couch while she is a niddah. The couch has separate sitting and leaning cushions
If the couch has separate cushions and they cannot feel the other ones movements, then it is permitted. Sometimes however if there is a mattress of springs underneath the cushions, then when one moves the other will feel their movements.
Shiurei Shevet Halevi 195-5 (11) D:H B’safa.