Another is called Klip Klamp. These are 'U" shaped clamps w/ 4 adjustmets. Used in making hanging tile ceilings. Get at any large construction supply/hardware store. soft to Owie!
If/when you want to make the clothes pins meaner, cut/sand off the corners. One at a time. Thus keeping the same PSI, but in a smaller area. I have three sets of pins. One normal, one dipped in red stain meaning one corner, and one dipped in black, both corners gone. OUCH More yet? Glue the hook pad of Velcro into the jaws.
Have fun.
Fred Norman