There is only one size but the models have two different heights. The Original (High) and the new Low.
Original: Best suited when the height of the seat below or the table can be adjusted. Movements are more active. Health effects more effective.
LOW: Suitable when you cannot adjust the height of your seat or table. There is less movements. Slightly easier to use.
Both have almost the same feeling  and they are soft and comfortable to use. You can estimate the appropriate height from how much your elbow can rise. These below dimensions are measured when sitting on the saddle chair.

HOW TO CHOOSE THE FABRIC?

The fabric cover cannot be removed.

Wash the surface with water and detergent.

There are different fabrics:

• 100% WOOL  It has all the advantages of the wool. Natural material, in hot temperature it is cool and in cool temperature it is warm. No pilling.  Cleaning with cool water and gentle detergent.

• EASY TECH  It is easy to clean. Cleaning with warm water and stronger  detergent. You can also use a brush.