We have been looking for a good mattres(king). I have back issues and we both sleep on our sides, especially me turning and tossing around a lot. We are looking for a extra firm mattress. I was sold on the Simmon Exceptionale for a while now as I had tried it a outlet store and really liked it. But am not finding it now. Our current mattress is sagging badly in the middle spots. We are also going with a platform bed now(no boxspring).

I can really use some recommendation please. We have a queen Sealy Posturepedic Park West  for our guest bedroom and I like that too. But I want to make sure I make the right choice this time and don't repeat my mistake from 6 years ago. Also would it be better to get a Latex mattress. Do we get extra firm in latex mattress? Would really love recommendations for either coilspring/latex. 

Need to buy it by Monday and get this done with it, otherwise its surgery for me :)  Appreciate the help here.

Regards.