Stability cushions are small because their function is to pose a balance challenge. It would be easy to catch yourself and move to another spot on a larger cushion, but it removes the challenge of trying not to fall. Having a larger cushion also causes a wider distribution of weight — so again, it’s less challenging than a smaller one. If you want to get a stability cushion where both your feet fit at the same time, opt for a foam model, as they tend to have a bit more space than round or oval ones.