There’s probably not much to add to your conversation as you have covered all the “moving parts” except for …
As you probably know … mattresses.net is a member of this site and listed as one of the best sources of various components and toppers (post #4 here). This topper is exactly what they say it is and is great value. They had another similar value before this one (a zoned Dunlop topper) that is now sold out.