This mattress doesn't feel like your standard plush spring or pocket coil mattresses, the top 2 ir 3 inches are pure plush and sink in very easily until you hit a firm layer. 
I initially thought I had made a horrible mistake ordering a firm instead of plush but it is just how foam mattresses are. 
Very supportive, hugely comfortable after getting used to the weird sensation of sinking weightlessly onto a firmer layer but I wouldn't go back to springs if you paid me. 
We have the king mattress and be prepared for some heavy lifting, it took everything I had to move the mattress onto the tall frame. (as a reference I'm a 270lbs gym junkie) do yourself a favour and get someone else to give you a hand moving it.