Research the mattress models that are available in your area. Remember, you shouldn't buy a mattress unless you've tried it out first. Some common brand names include Sealy, Tempur-Pedic, Select Air, Simmons and Stearns and Foster.
Make a record of the prices offered by the various mattress brands and retailers. For a new mattress, you can pay anywhere from less than $1,000 to more than $4,000, as of 2009. Prices are determined more by brand and model than by size, but within each model, you should expect to spend at least $100 extra as you move up each size, whether it's from a twin to a full, or a queen to a king.
Become familiar with the various comfort options available through each mattress brand and model. The wording used for the various models will vary by brand, but what you're looking for is how soft or firm the mattress model is.
Look for differences in traditional spring mattresses and memory foam mattresses. The memory foam mattress will fit with the shape of your body, while the spring mattress does not adjust the same way. What you choose will depend on your personal comfort preferences.
Try out the mattress models you're considering. That is, pretend to sleep on them in the store. Lay in the position you sleep in for at least five minutes. If you start to feel uncomfortable, then that model probably isn't a good fit for you.