This is the second version of my single joycon controller grip. It has more room and a universal design. It accepts both of the controllers (left and right), and they fit pretty well. You can wrap some blue tape around the top knob to make the fit tighter. It also has room for the straps, therefore you can enjoy the nice shoulder buttons on the strap.
The supports are kind of insane on this, but once you remove them and sand the bottom down, the grip feels really good. There shouldn't be any sanding needed for the area where the joycon goes since its the top of the print.