Hi slartybartfast,
The issue of dust mites in a mattress and their connection to allergy symptoms is very controversial and there are no specific answers to your questions that I’m aware of.
There is some information about dust mites in post #2 here including a link to a study that indicates that even effectively reducing the exposure to dust mite allergens in a mattress by itself isn’t enough to reduce the allergy symptoms that are the real reason behind these types of questions unless it is part of a more comprehensive strategy of controlling dust mites that includes other elements as well (pillows, humidity, vacuuming, hepa filters etc).
I also believe that which type of foam or even which type of mattress components (such as an innerspring) is most resistant to dust mites misses the larger point completely which is that dust mites will tend to accumulate on mattress covers or bedding and not as much inside the mattress and that regardless of the type of mattress you have that a strategy or regular vacuuming and washing in hot water along with encasing the mattress with a dust mite resistant allergen cover is a much more effective strategy to reduce dust mite populations in a mattress than focusing on the type of foam materials or components that are in the mattress itself.
There is also more information about dust mite control and mattresses in some of the information and studies linked here and here and here as well.
Phoenix