Yes you can. Enlightenment would indeed be a strange thing if it could only be attained in a few postures! Chairs, benches, cushions, couches, and beds are fine support for meditation. How you sit is far less important than whether the posture supports mental alertness. Westerners tend to grow up sitting on chairs, not squatting on the floor. I will help you discover how to find the best posture for your body.