Cotton is world's most widely used natural textile material. Today it is usually used in upholstery layer and surface padding of mattress / ticking. Cotton is so distinctive, because of excellent ability to breathe and to absorb moisture.

Pros of cotton:
Excellent surface properties, good comfort level.
Zero allergy risks. If you have allergy to synthetics, definetely choose mattress with cotton surface.

Cons:
Relatively high price, due to natural source of material

How to select good cotton mattress:
I have no special suggestions on how to select good cotton mattres. Just select mattress with natural white surface with no paints on it.

Conclusion:
Cotton is excellent material for mattress coverage. It is really one of the best material for such purposes.