Here are some good options for buying a physio ball online:

• USA – Recommended products (or elsewhere in the world)
• Canada – Recommended products

Tips: Look for a ball with a pump included – foot pumps are nice to have. Suggested sizing:

• Height 4′-8″ to 5′-6″: 55cm ball
• Height 5′-7″ to 6′-1″: 65cm ball
• Height 6′-2″ – 6′-8″: 75cm ball