To my knowledge, the absolute lightest shoulder rig for a J-frame has to be a Null City Slicker. It's all plastic (polymer), and will accomodate a J-frame of any barrel length. I have one and use it quite a bit when I elect to carry in a shoulder holster. The drawback is the drawstroke is definitely unique, and requires practice. The upside(s) are its lightweight, easy to keep clean, very thin and unobtrusive (makes it easy to hide under a light shirt as a cover garment), and can accomodate a 2.0 inch or 3.0 inch barreled J-frame without any problems or adjustments. Ken Null has a website where you can learn more about his products.
Best of luck,
Dave