Hi Crispin

I am something of a foam expert now. Can advise on various thicknesses and grades.

Foam grades are expressed XX/XXX. The first number is the density. The higher the number the greater the density and therefore better quality.

The second number refers to the softness. The higher the number the harder it is.

Examples:

30/160 medium quality, medium firm, good for sitting and sleeping

50/125 high quality, soft, good for sleeping

I have samples of loads of different foams which you could try out it you wanted. And I've got memory foam too, so you could see how that works.

Foam is cheaper if you get it in full sheets or half sheets and cut it to size. But if you don't fancy cutting it, most foam suppliers will cut to size for you.

Standard boat mattress 4" thick. Standard back rests 2" thick. 'Luxury mattress 5" thick. You've got plenty of room on your boat so you could easily go for 5" foam.