I recently got a Serta St. Charles Eurotop mattress and box spring - aside from the huge increase in size from a Queen to a King (Not Cal King, narrow piece of shit) - its super comfortable.
The one thing I found out is that its really, really, really hard to judge a mattress just by brand or model - Brand seems be an indicator of general or usual quality and longevity versus how comfortable it actually is. I got a bunch of reccomendations on mattresses and every one I tried was uncomfortable as fuck. Finally, a lady there said try this one and it was the one.
Go to Macys or a mattress store and lay on every fucking one before making a decision.