For a couple, you only technically need two pillows, but it's nice to have four so you'll have different options depending on how you're feeling (and allow yourself to prop yourself up for reading at night or drinking coffee in the morning). Some people also like to have decorative throw pillows on a bed as well—it can be a fun way to dress up your bed with contrasting textiles and round, square, or bolster shapes. Just don't go overboard with pillows or they'll end up spending more time on the floor than on the bed.