Re: Sleeping preference?
Foam is great, just make sure that it is in good shape (it deteriorates over time). You can unzip most boat cushions to check out the foam inside.
Remember that expensive Tempurpedic mattresses are simply 6" of high grade 35lb density foam with 3" of memory foam on top. You can easily replicate that on a boat by adding a memory foam topper to your boat's foam. They are cheap from sources like overstock.com. I like to use the egg-crate style (lying on the flat part, egg crate facing down) because it helps the bed breath and dry out when you aren't in it.
Our specific bed recipe is:
HD36-HQ base foam mattress in 4" from Foam Factory
Eggcrate memory foam topper in 3" from Overstock
A sheet over the whole thing. Make your life easier and use flat sheets, not fitted. A queen sheet fits over most V-berths
Then another flat sheet and other bedding of your choice on top. This gives us comfort very close to what we have at home.
I bought standard sized toppers and foam mattresses and cut them to size. Memory foam topper can be cut with heavy duty scissors. The foam mattresses were cut with a cheap electric turkey carving knife. Our V-berth and quarterberth cushions are in two pieces, but we made the toppers bridge that so you can't feel the gap in the cushions while sleeping.
Our boat has a double width quarterberth, a V-berth, and two settees. We've used all of them successfully for sleeping, but get the best night's sleep on the quarterberth because it provides the largest bed area. Guests seem to prefer the V-berth because it is well above the waterline (some people are uncomfortable sleeping right at the waterline) and has the most accessible ventilation.
To get used to sleeping on the boat do some easy overnighters (even just staying in your marina) before heading out on a longer cruise. I often stay on my boat the nice before a race or long sail, and doing so gives me a chance to experiment with different setups.
boats that I sail on regularly: Pearson 28-2, Rondar 505, Yankee 30, Blanchard Junior