Hi gary,
Welcome to the Mattress Forum! … and I’m glad you found us 
[quote]I need a mattress for my sailboat which I live aboard. I can handle a queen and a height of 6" to 7" only. (I will cut it down on the length and bevel one side with the help from a local upholstery shop) .
I’m 5’ 10" and 230lbs. I’m a side sleeper and sometimes sleep on my stomach and back. In the past, I have used a medium firm traditional mattress and the current poly foam on the boat would be similar to medium firm but is now "bottoming"out.[/quote]
If you are attracted to the idea of designing and building your own DIY mattress out of separate components and a separate cover then the first place I would start is by reading option 3 in post #15 here and the posts it links to (and option #1 and #2 as well) so that you have more realistic expectations and that you are comfortable with the learning curve, uncertainty, trial and error, or in some cases the higher costs that may be involved in the DIY process. While it can certainly be a rewarding project … the best approach to a DIY mattress is a “spirit of adventure” where what you learn and the satisfaction that comes from the process itself is more important than any cost savings you may realize (which may or may not happen).
If you decide to take on the challenge then I would either use the specs (if they are available) of a mattress that you have tested and confirmed is a good match for you in terms of PPP as a reference point (the same type and blend of latex in the same thickness and firmness levels and a very similar cover which can also make a significant difference to the feel and performance of a mattress) or use a “bottom up” approach (see post #2 here).
I would also keep in mind that there are also no “standardized” definitions or consensus of opinions for overall firmness ratings and different manufacturers can rate their mattresses very differently than others so a mattress that one manufacturer rates as being a specific firmness could be rated very differently by another manufacturer. Different people can also have very different perceptions of firmness and softness compared to others as well and a mattress or a combination of layers that is firm for one person can feel like “medium” for someone else or even “soft” for someone else (or vice versa) depending on their body type, sleeping style, physiology, their frame of reference based on what they are used to, and their individual sensitivity and perceptions. This is all relative and very subjective and is as much an art as a science. There are also different types of firmness and softness that different people may be sensitive to that can affect how they “rate” a mattress as well (see post #15 here).
[quote]I have tested the Pure Latex Bliss "Natural"mattress at a local retailer. It’s the only retailer that offers latex so I’m limited to physically reviewing any others. The “Natural” model felt good for me because it was soft enough and still very supportive. The “Beautiful” model felt a bit too soft (less supportive) but was also close to excepting.
Liked the Natural better?[/quote]
The Pure Latex Bliss Ultimate collection uses blended Talalay latex which they call “natural” even though it’s a blend of about 70% synthetic rubber and 30% natural rubber. Their Organic collection uses 100% natural Talalay (which doesn’t use any synthetic latex in the formulation) but it’s not organic (there is no Talalay latex that is certified organic). There is more about blended Talalay vs 100% natural Talalay in post #2 here.
If you are planning to order from Foambymail (FBM) then I would read this post and this post and this topic (about their polyfoam and sources) and this post (presumably from a past employee) before buying anything or considering them as a reliable supplier. They don’t sell Talalay latex … they only say they do … and I also wouldn’t consider their latex ILD ratings to be reliable.
There is also more about the general differences between Talalay latex and Dunlop latex in post #7 here.
I don’t have any specific suggestions because you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and individual preferences and sensitivities involved to be able to use a formula or for anyone to be able to predict how a specific mattress or combination of layers will feel to you or to make a specific suggestion or recommendation about which mattress or combination of materials and components would be the best “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) based on specs (either yours or a mattress) or “theory at a distance” that can possibly be more accurate than your own careful testing or personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
The specs of the PLB “natural” mattresses are in post #2 here and there is also more about the different ways that one mattress can “match” another one in post #9 here but a single core mattress or a mattress that uses two layers with a thin comfort layer that is only 6" to 7" thick that uses a different type and blend of latex can’t really be meaningfully compared or “matched” to another mattress that uses a different type and blend of latex with different firmnesses and different layer thicknesses.
Every layer of a mattress will affect the feel and performance of every other layer both above and below it and there are also so many different “specs” that will affect the feel and performance of a mattress that combine together as part of the overall design of a mattress that makes one mattress suitable for one person and not another that ILD by itself can be somewhat misleading because it isn’t the only specification that determines the feel and performance or firmness level of a mattress (see post #2 here).
If I was in your shoes I would use as much total thickness as you can because it would give you more design flexibility and if 7" is your maximum I would probably tend to use a 4" - 5" bottom layer in the range of about 36 ILD and then a 2" to 3" softer comfort layer in the range of about 24 ILD. The thicker comfort layer would be softer than the thinner comfort layer because with thinner layers you would “feel” more of the firmness and the transition into the deeper layers below it. While in general terms a thinner mattress will tend to feel firmer than a thicker mattress (see post #14 here for more about the effects of thickness) … I would be cautious about using ILD’s that are either too soft (lower than about the lower 20’s or so) because of your weight and because you spend time sleeping on your stomach which can both make softer layers (or softer comfort layers that are thicker) more risky in terms of alignment issues. If you start with a 4" support core then you would still have “room” to add either a 2" or a 3" comfort layer on top of it depending on whether one turned out to be a better “match” for you in terms of PPP than the other one.
With any DIY mattress where you can’t test the specific combinations before a purchase I would also make sure that you are comfortable with the exchange/return options available to you after a purchase to help offset the higher risk of buying layer combinations that you haven’t tried that don’t work out as well as you hoped once you have the chance to actually sleep on them.
Phoenix