Here's a comparison with a Walmart queen sized Mainstays pillow with medium support. I've had this one for about four weeks now and it's already broken in. I feel though that this pillow isn't as fluffy or poofed up as when I first bought it.
Between the two, the Simons is smaller, thinner and stiffer. However, the softness is felt gradually as the weight of your head sinks in to the pillow and will sink in just enough to support your head. The Mainstays on the other hand will sink in more immediately. Don't be fooled by the thinness because there's still a lot of pillow left between your head and the bed to provide support.
I would argue that this is a 9/10 pillow for back sleepers like my folks.
Edit: I used a 2L bottle of juice to put some weight on them but I think it's too light to simulate the weight of a head. Notice how the neck of the bottle is completely sunk in the Mainstays pillow and still somewhat elevated on the Simons pillow. A rounder and heavier object like your head it would sink in more and your neck will be cradled just enough on the Simons pillow.