Hi frederixx,
The Aria would be similar to the Tempurpedic Cloud Supreme and the Harmony would be similar to the Harmony inspiration so you could test both of these mattresses locally to see which one was the best match for you.
If you can’t test them in person then I would talk with them on the phone so they can talk you through your comfort choice. I wouldn’t use emails to make comfort choices (see post #4 here).
Phoenix