Hi Redsaffron,
There is more information and sources for wool mattress toppers in post #3 here (which includes Cozy Pure).
There are many differences between wool toppers including the type and species of wool used and the raw material cost, the type of layering and construction, the specifics of the cover and the tufting, any return policies or other benefits that go with each purchase, and other factors besides just the weight of the wool that would all be part of the cost of a wool topper. I think that all of them are good quality choices from reputable companies and all of them have fair prices.
Phoenix