M_Boats: New Cushions

So I am looking to get new cushions made for the inside of the M15 and I was wondering if anyone could give me their insight on a few questions. 1.) Do you think I need "Marine" foam? What is the difference between that and foam you'd see in a couch cushion? 2.) The upholster is asking if i'd prefer 3 or 4 in foam....Any thoughts on what is better to sleep on? I am also exploring the possibility for having cushions being made for the cockpit. Has anyone on the forum here done that and if so could you give a little background on what specifications you had them made to and how you like the cushions? Thanks! -Ted