So, you've decided to become a yogi. Now what? For starters, get some yoga clothes and a yoga mat. Your clothes should be comfortable and move with you(and cover all parts). Try clothes made from bamboo, hemp or organic cotton which are grown and produced in ways that are gentler on the planet.
As far as mats go, buy one that doesn't contain polyvinyl chloride, or PVC. The manufacturing of these mats releases harmful dioxins into the air and water, and the phthalates used to soften them may mess with your hormones. Who needs that?