Start saving your cereal boxes! (And oatmeal, and envelopes, and Lean Cuisine!) Behind each piece of fabric is any random box, as seen here. I considered making them all match size-wise, but really thought the mismatched pattern was more fun. Because the boxes are different depths, this mattress stack ends up being a bit tall - typically taller than your average storytime guest while seated on their bottom. I think that height makes the story more enchanting - truly "bigger than life" to them.
As you tell the story, you'll place your pea under the first box. It's never tipped over on me, but just practice to make sure you get it balanced. My little pea is made of play-doh and left to dry (sorry, the picture isn't great.) Once dry, it was painted with fabric paint (no reason...just what I had) to give it a better green color. The princess on top is a random (old) princess doll that we happen to have at our Library. I am sure you have one, too. You could also use a Barbie, if you had one of those sitting around somewhere.
If anyone would like the text that I use when telling the story, I would be happy to send it to you (just leave me a comment). It is a very simple text that emphasizes the Prince's search for a real Princess. In the pouring down rain, a girl comes to the door claiming to be a princess, and the mother of the prince (skeptical) goes to hide the pea beneath all the mattresses -the best mattresses, covered in her finest fabrics. You can have the kids help you make rain and thunder for the storm, knock on the castle door, and feel the soft fabrics of the mattress.
This story has been a huge hit whenever I use it. It is very appealing to young gradeschool class visits, as well as storytimes for the preschool age. It is a good reminder of how powerful storytelling can be...no book, just the power of a great story.