Sometimes you are even paying the salesperson who sold you the mattress because the brand name companies will pay the salesperson bonuses for selling their mattress. First the mattress should look rectangular. Look at a company's pillow top model, it should match up with the edge of the mattress. The stitching on the edges should be close together. If the stitching is far apart or the stitches are long, in later years it can cause the panels to stretch and make the mattress feel soft.
Coils are important to a point.
You should also consider the gauge of steel. The lower the gauge, the stronger the innerspring. Most promotional mattresses may actually be foam or have a low coil count such as 231. When you look at mattresses with a high number of coil counts that exceed 660, the gauge of steel used is 15 gauge. At Midwest Bedding we install metal side supports on the edge of the innerspring.