What Can Be Placed Behind A Sofa So Heat Register Doesnt Heat Up Fabric

This is our new house, and I wanted to put the sofa along the back wall, facing the fireplace where I'k hoping to add some built-ins and mount the TV. But, the big vent forth the back wall I believe is an air return vent, for our HVAC, and the realtor said we shouldn't cover it. Is that true? If so, What are my options? If absolutely necessary, I could put a long narrow sofa table over the vent, to go the sofa at least partially off the wall to allow for apportionment, (run into photo case) but that is certainly not platonic. If the sofa is a few inches off the ground over the vent, would that let enough menstruation?