Serta's Modern Series is a collection of thinner profile, all foam mattresses with cooling features, all at incredible prices. Available in three comfort levels to offer the right feel for all users. Serta® PureComfort Gel Foam provides cushionin and cooling along with the Serta® CoolWickTM Breathable Cover, keeping you cool and comfortable all night. The Firm "Comfort" firm is a good mattress for a stomach or back sleeper.