Another way to layer your bed: one extra long pillow. Amber Interiors uses this trick, and I recently purchased an extra long pillow for my bed.
Why is this popular? It's easy. If you don't have room for/time for 5 extra fluff pillows on your bed, just throw on one extra long lumbar decorative pillow, and you're good! Simplify your life.
What are the requirements? At least 30" across. Possibly longer.
Emily Henderson has a nice post and a nice shopping list on the extra long pillow for your bed.