Decide what you can spend. When selecting a mattress, there will always be a better one that is out of your budget. Tell your salesman what you are willing to spend and have him lead you to that area.
When deciding on firmness, take into consideration how you and your partner sleep. If you sleep on your back, go with a softer mattress; your shoulders and rear will fall deeper into the mattress since these body parts weigh the most. When they sink in, your body will be aligned. If you sleep on your stomach, get a firmer mattress so it presses against your body, keeping it aligned. Side sleepers can go either way, but they usually prefer a softer mattress. With a sleep number bed, your partner can have a firm bed and you can keep it soft.
Count the coils. If you are selecting a queen-size mattress, try to get a coil count of 700 or more. The more coils, the more durable your mattress will be.
Choose a foam. Latex and Visco are going to be the most durable and are consequently the most expensive. These foams start at about 1/4 inch in thickness.
When selecting a new mattress, some companies to keep in mind are Sealy, Restonic, Serta, King Koil, Sterns and Foster. Most of these brands can be found in any furniture store and even some department stores.