This 12" mattress is absolutely fantastic! We use it at the "medium" softness side. It is soft and comfortable, but one does not just sink in it. 
A word of caution about returns: The mattress is fairly heavy and it is  packed in vaccuumed plastic. Once you unpack it it expands and becomes quite large. If, for any reason, you decide to return it - good luck with packing it up! Also, with Wayfair, you will be paying for the return shipping.
However, besides the Caviat Emptor above, the mattress is phenomenal and we like it a lot!