Local stores near Hardeeville aren't the only way to shop! You can also find name brands from online retailers and get them shipped right to your door!
The firmness of a mattress refers to how soft it feels, and is a somewhat subjective measurement. Don't confuse this with the support it provides, as that's more a measure of how well it holds your back in position. Firm mattresses may provide great or horrible support, and the same is true for softer options. Find a blend that works for you!
Weight and body shape are a major thing you should consider in your choice. Your experience with a mattress may be completely different than someone who weighs significantly more or less than you. In general, heavier sleepers will need more support from a mattress to be comfortable, than a lighter sleeper.
The position in which you sleep can play a role in your choice of mattress: