There should be no gap under the three major areas that require support – the lumbar, between the shoulder blades, and behind the knees. The mattress should be snug against and conform to the body, providing proper “push-back” in the negative areas mentioned. The stomach should be flat, and the hips and torso should not sink down lower than the feet, which would indicate a too soft mattress. The spine is not flat, and the perfect mattress should conform to each individual silhouette, resulting in symmetry between body and product.