Shoulder mounts are great for stability, but they can be pretty pricey. This DIY project by TheJamesTheatre is better in both aspects—it rests on both shoulders for extra stability, and it only costs 8 bucks to make.
The frame is made of PVC with foam pieces from a pool noodle for cushion. All you need is a few connectors and the nuts and bolts to put it all together. You can find the full parts list on the About section on YouTube.
James also suggests adding some glue for stability and painting the whole thing black to make it look a little more professional.