Hi slartybartfast,
For the mattress part of your strategy I would focus much more on a mattress allergy encasement, pillow encasements, and an encasement for your foundation along with regular vacuuming of the mattress surface and washing your bedding in temperatures that are hot enough to kill the dust mites and their eggs than I would on the type of foam in the mattress which IMO based on all the reading I’ve done isn’t a particulary important part of the puzzle (although it’s a “straw man” issue that many mattress salespeople love to use to promote the mattresses they sell as soon as they know that a potential customer has significant allergies).
There is more about mattress allergy encasements in post #2 here.
Phoenix