Almost all sun loungers are made to be able to lay on your stomach, and the Ostrich and GoPlus options even have cutouts in the lining to make laying on your stomach even more comfortable. Keep in mind, though, that not all pieces are made to lay completely flat. There are some options out there that can only get down to about a 25-degree angle, which might be a little uncomfortable for stomach laying. Other options have a declined bottom half that also might make it difficult to lay on your stomach. If getting a tan on both sides is the endgame here, be sure you check to see if the design that you land on can lay completely flat.