I prefer my foam mattress aboard to my high priced inner spring one at home (or perhaps I just like sleeping aboard :O).
I had a local canvas
maker make me a custom foam mattress for $300 (foam and cut, already had the canvas). It is fantastic. I went to her shop, learned about the different qualities, thickness, densities and firmness of different foams (there is a lot to chose from). Then tried some samples out. I went with mattress quality foam treated for moisture resistance (marine grade?).
So, I had her put together a mattress for my vee berth of 4" medium density foam topped with 2 inches of low density foam. WOW. It is fantastic. It is as comfortable and conforming as 'swedish' foam for a fraction the price
. It also gives me plenty of support and does not 'bottom out'. All this can be 'dialed in' by testing different pieces of foam. You can put any combination together you want, any thickness you want. Could get an 8 inch mattress of 2" low density, 4" medium and 2" high density. Could be 3" low, 3" medium. etc etc. Anything. Could not be more custom.
The other advantage is that if I ever don't like it or get tired of it...I can just go get another piece of foam cut to fit the canvas
Hope this helps