You've been to the store and you've tested out a lot of mattresses. Hopefully you’ve found at least one mattress that you love! But don’t (repeat, don’t!) close the deal on your first store visit. You’re going to be living with this mattress for the next 8 to 10 years, so it’s worth taking an extra day or two to make sure you’re getting a quality product.
Read the product ratings and reviews of the model or models you liked, paying particular attention to feedback about things it's hard to evaluate in the store, such as the model’s comfort and durability over time. Think of it as doing a background check—you’re confirming that owners of that mattress or brand of mattresses have been satisfied with their purchase. And if they haven’t, make sure it was for reasons that you feel don’t apply to you (such as comfort or support needs different from your own), rather than for reasons that might affect your decision (such as poor durability).
This is also the time to scope out the details of the manufacturer’s warranty for the model you are interested in. And you may want to consider the manufacturer’s reputation, based on customer reviews—do they have a track record of responding to and resolving customer complaints and warranty issues? Or do they have a reputation for “buyer beware”?