I'm usually in a hurry to find an allergy proof mattress cover and would settle for one made with some sort of latex barrier (therefore not breathable and leads to being too hot overnight and not a peaceful night's sleep), but decided to find one on line- 

I was happy to find this website that offered pure cotton ones. 

I just received this yesterday and put it on my bed. The weave on the fabric is tightly woven and the product seems to be very good quality. I am hoping this will keep the dust out and last a good long time; I think that it will.