You can just start out where lots of folks start out: Do the basics by following along with videos from established and accessible instructors (e.g. Rodney Yee,

You can just start out where lots of folks start out: Do the basics by following along with videos from established and accessible instructors (e.g. Rodney Yee, Seane Corn). These are folks from the DVD era that are still active. Pleasantly, Yoga is a relatively established practice with minimal churn/disruption to the state of the art. Yoga is great for core strength, getting rid of back soreness, and gently improving flexibility. You'll also learn about your own body and develop greater self awareness when moving. Just take care that, though the risk is lower, you can still injure yourself by overdoing it. Listen to your body along the way.