Do I have to sit cross-legged, or can I meditate on a chair?

a chair is fine; what matters is a steady, comfortable seat with the spine upright.

Patañjali’s definition of āsana is just three words: “sthira-sukham āsanam” — the posture should be steady and comfortable (Yoga Sūtra 2.46). The Bhagavad Gītā (6.11–13) describes a clean seat, neither too high nor too low, with the body, head and neck held straight. Nothing says the legs must be in padmāsana.

Sukhāsana (simple cross-legged), ardha-padmāsana and vajrāsana are common on the floor, often on a folded blanket or cushion. If knees, back or age make that painful, sit on a firm chair with both feet flat, back away from the backrest, hands resting on the thighs.

Keep the spine upright but not stiff, relax the shoulders and jaw, and close the eyes gently. Lying down tends to bring sleep, so it is better kept for relaxation or for those who are unwell.

Source: Yoga Sūtra 2.46; Bhagavad Gītā 6.11–13

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