Hi Sum,
I'm not an upholstery expert, but my father-in-law is(been his business for 45 years). He replaced all the cushions inside using Sunbrella (...he put me to work

). He had me cut the new foam(his son is a supplier....yes, I lucked out on all of this

) It was like a white, super whammy dyne foam....couldn't tell you the name, then had me wrap it in dacron(don't know the proper name for that.....batting?)My old, original cushions did not have it. It does make a big difference in feel, breathes, and installs in the covers easier,not to mention a bit cushier(is that a word?) He used some other foam (4 inch)for the V-berth that made sleeping on it literally like night and day(I'll ask him what the foam was if you want).
Plan on doing the cockpit this year. That fabric you have picked out looks like the outdoor cushion fabric he uses for pools and such. It wear well, has good fade resistance, and dries quickly. It just isn't the nicest stuff against bare skin. I need to get my bro-in-law to get some of that closed cell foam. He has this HUGE horizontal band saw that he cuts it with. Not sure about color for cockpit yet.
C Ya,
John