Your pillow will be about 16" by 16". You will need 3 different prints but they should complement each other because you will be making a patchwork pillow. You should buy between 1/3 of a yard of 3 different cotton print fabrics to make your pillow.
You will need a another 1/2 yard for the back of the pillow
You will also need to buy the stuffing for your pillow.