Begs the question of how best to do the numbering. The sequence yaw, roll, yaw, roll will give a full rotation without requiring that the mattress ever be flipped length-wise (pitch). But this isn't a golden rule because you have to remember the last operation. Hence, you can start with any orientation, label the upper right corner 0, yaw, label it 1, roll label it 2, yaw label it 3, roll done. Now all you have to do is remember to flip the mattress. :)