Open Coil mattresses have separate springs arranged in rows and interconnected by a spiral wire and an outer rod for strength. The more springs, the greater the amount of support. Pocket Sprung mattresses also have individual springs.  Each is contained however, in an individual fabric pocket.  The springs work independently, supporting all parts of your body in contact and providing all-over support.  Again, the more pocket springs, the more even the support.
Memory Foam (also called visco-elastic polyurethane foam) is firm when cold, but softens in response to heat from the body. This enables a memory foam mattress to mould to your body's shape giving the most comprehensive spread of support. Higher density memory foam takes a few minutes to react, whereas a lower density foam is also pressure sensitive and will mould more quickly to your body shape.  

Choosing a Mattress

Sleep is essential to feeling good and good health. Choosing the right mattress is a great start to healthy sleep, but with so many choices, the task of selecting a new mattress can be overwhelming. Here are somer tips to help you make the best decision.
1. Comfort
Take time shopping for a mattress. Try several different types, taking the time to lie down on them and turn over on them. Spend several minutes lying in your normal sleeping position – 5 to 10 minutes should be the minimum time spent on each bed. If you have a sleep partner, make sure you shop for your new mattress together. Lie on the mattress at the same time. Check for uncomfortable pressure points as well as partner movement. The amount of surface cushioning to have is a matter of personal preference.
2. Support
It used to be said that a firm bed was better for your back.  This given way to a more correct view that comfortable, correct support is best for optimum sleep. Firmness and support are not the same things. In order to keep your spine in correct alignment, you need to choose a mattress that follows the natural contours of your body. When a mattress is too soft or too firm, it creates pressure points that cause the muscles to strain to keep the spine in a natural position. Your body has to work hard throughout the night, leaving you feeling tired the next morning. A good mattress supports the back and allows the muscles to rest and rejuvenate during sleep.
3. Your Sleep Position
Different mattresses will be more comfortable depending on the position you sleep in. Sleeping on your side places increased force on your shoulders and hips, causing pressure points. Side sleepers may prefer a mattress with more surface cushioning.
A back sleeper’s weight is usually distributed evenly over the mattress surface. However, without proper support, regions of the back (such as the lumbar area) may undergo excess strain as it works to support the spine’s natural curves. Mattress systems with extra cushioning or adjustable support mechanisms may be the most comfortable choice.
4. Your Needs
For best sleep, it is generally recommended to have the largest sleep surface your bedroom will allow. Choose a mattress that is wide enough to accommodate the sleeper (or sleepers) comfortably and several inches longer than the (tallest) sleeper.