Hi mutty62,
I would also include OMF as a priority option in most areas of the country where they have a store.
You will need to use “best judgement” about which of these would be most suitable in combination with your memory foam topper in terms of PPP because you won’t be able to test the combination in person (unless you drag your topper into the store :)).
I would also make sure you find out the specifics of the layers inside both of them so you can also compare them in terms of the quality of the materials.
They are also two sided which will make both of them a more durable choice as well (see post #3 here).
I’m looking forward to finding out what you end up deciding.
Phoenix