Shop Serta Serene Sky 11 Plush Mattress- Queen online at Macys.com. Serta’s Serene Sky™ 11 Plush Mattress offers an unbeatable value from a trusted name. Exceptionally soft, this mattress is ideal for side sleepers who enjoy a cushioned feel. Cool Twist® Gel Foam works to create a cool sleep surface which is essential for a more restorative sleep while the 805 Individually Wrapped Coil System provides contouring cradling support. Finally, BestEdge® Foam Encasement ensures that you will not have a sinking feeling at the edge of the mattress.