Hi LuvMyGSDs
There is more about the pros and cons of different types of mattress protectors and some examples of each of them in post #89 here that should be helpful.
The wool mattress pad you linked has 300 gsm of wool which is about 9 oz/sq yd so most people would notice “some effect” of the feel of a mattress but “how much” of an effect and whether any specific person would consider the effect to be detrimental or beneficial would depend on the person and on the specifics of the mattress.
Their prices are also significantly lower than others that carry the same product so I would also call 45th Street Bedding to make sure that they are an authorized dealer and are selling new products.
Phoenix