Breathable, natural materials like linen and cotton are my favorites. They're easier to clean than silk and feel good against the skin. I love florals and stripes, too. You can mix the designs if you have a color that ties the pillows together.
I don't care for a ton of pillows on the couch. If you're collecting, that's one thing, but too much of even a nice thing makes an object lose its uniqueness. Pairs create balance, and a single in the middle of a love seat will make the pillow seem special."