Have you tried calling the manufacturer Sleep Science or Costco?
It’s possible that nobody on the forum has purchased one (or if they have they haven’t seen your post) because the mattress doesn’t meet the minimum guidelines that are suggested here for a memory foam mattress. There is more about the Emma in post #2 here and the posts it links to.
I don’t know the specific size of the Emma after it’s compressed but typically there would be no problem with narrow stairs and hallways. A google search (or a YouTube search) on “compressed mattress” or “roll packed mattress” will turn up some videos of other compressed mattresses which can give you some sense of their compressed size (I didn’t find any specifically for the Emma).