Pink foam board from Home Depot, cut to fit around fireplace. I duck taped it together (underneath as well). Then, I covered it with quilt batting (folded to form layers). Lastly, I got some cheap fabric from hobby lobby and hot glued it underneath.
Need to install a baby gate, but don't want to drill into the wooden stair banisters??? Cut a couple of 2x4's to the height of the banister, paint,and secure with heavy zip ties. Then just add the baby gate hardware to the new piece of wood........D.