My wife and I currently liveaboard our Hunter 31 (1984). A good nights sleep is essential, and our 30+ year old worn out v-berth cushions weren't cutting it. We sunk straight down to the fiberglass! The covers were newer though, so I decided to keep them. They were sized to fit 3.5" thick foam.
I did quite a bit of research online about what makes a good mattress, and also some trial and error in purchasing foam. In the end we are very pleased with how comfortable our foam is and it wasn't too expensive either. We purchased all the foam through foambymail (which appears to be the same company as thefoamfactory.com).
The basic premise behind our v-berth mattress was 3 layers: hard base (LUX HQ 1.5" thick, 50lb ILD), medium middle (HD36 HQ 2" thick, 35lb ILD) and soft top (super soft foam 2" thick, 12lb ILD). Keep in mind that ILD is "firmness," whereas density refers to how heavy the foam weighs (heavier density = higher quality). A very heavy foam can be very soft, and a very lightweight foam can be very firm, but would be inferior quality.
Here is the exact size/price breakdown of what we purchased:
1 Lux High Quality Foam - Full - 54" x 75" x 1/2" 14.99
1 Lux High Quality Foam - Full - 54" x 75" x 1" 28.99
1 HD36 High Quality Foam - Full - 54" x 75" x 2" 53.99
LABOR TO GLUE THE LUX-HQ & HD36-HQ PIECES
TOGETHER TO MAKE, (1 PC) 54" X 75" X 3-1/2" ($40)
That made a 3.5" Full size foam piece which we cut in 2 V-wedges to fit our V-berth cushions and they fit just right. Then, on top of our cushions we added the following topper: Super Soft Foam - King - 76" x 80" x 2" 53.99
Total foam cost: $191.96 w/ free S&H. This page shows their price breakdown:
http://www.thefoamfactory.com/mattress/conventional.html
The reason we got King for the topper but Full for the base was because Full is all you need to cover the v-berth area if you're willing to cut the foam diagonally, which was fine for filling the old covers (our length was slightly longer than the Full 75", but for the "pointy" end that was short I just cut a small piece from the scrap to put down there and it filled the cover perfectly). For the Hunter 31 at least, King is what you need if you want to cut a single piece of foam to fill the V-Berth. I wanted our topper a single piece.
We did try egg carton foam as a topper at first since it was less expensive, but it didn't work. The 1.5" thick egg crate did basically nothing and so the bed was too firm.
All the foam was cut with a reciprocating cutting knife which went through like butter. However, when cutting foam in the 2" or less thickness I found we could get away with sharp scissors.
If we were making new covers for the V-berth, I would have foambymail glue the 3 layers together and use even numbers (2" thick for each layer) and have the new cover made to 6" thick. One thing to keep in mind this could reduce your head height in the v-berth if your original mattress was less than 6". If vertical space is at a premium some compromise could be made (such as having the middle layer only 1" thick). However, what I read was mattresses for adults should be at least 6" thick. Ours is 5.5" thick and I don't sink down anywhere near the bottom. It feels like I float on the plush topper! Btw, I'm about 180 and 6' tall, my wife is much shorter and lighter.
On the plus side of having a thicker mattress, you get more surface area because the hull is angled outwards as it goes up. For us, going from 3.5" to 5.5" thick gave us extra room in both the width and length of the V-berth. I also intentionally cut the topper even little oversized so it rides up an inch or so on the sides of the hull which gives even a little more.
For our bedding arrangement, we cover everything with a Queen fitted mattress cover, and then cover that with a fleece blanket and finally a quilt.
I shied away from memory foam because firmness changes based on temperature, and I figured there may be wide temperature variation depending on time of year, location of where we're cruising and I didn't want it to be comfy in winter and too soft in summer, or some such. Also, it is usually hot here in Florida, and one complaint about memory foam was that it tends to make you sweat more. However, many people use memory foam and love it.
As an aside, we found 50 ILB was the correct firmness for our 3.5" thick seat cushions. With 35 ILB we just sank to the bottom.
