You could try googling for reviews, might give you an idea of other folks opinions too.
They are Stearns and Foster plush pillow top mattresses. The basic one which if I remember correctly is called the entry level one.
I’ve only sat on a few mattresses over there when we were lucky enough to be given a private tour of the hotel after it opened, I felt them to be firm but not overly so.........of course our opinion on firm might be different to yours.