If your zafu (meditation cushion) is too flat, your legs can bend at an angle that cuts off circulation, causing your feet to go numb. Unfortunately, zafus inevitably flatten out over time as the canvas cover stretches and the cotton stuffing compresses, leading to numb feet. However, there is a fix!
My solution is to wrap a rope around the circumference of the cushion like this:
One or two turns of rope is sufficient; I just had a long rope on hand. It is actually possible to wrap too tightly, causing your zafu to be so tall that you start sliding off the front. Just adjust the tension in the rope until you find the perfect height.