Hi Martina,
A softer top layer is more pressure relieving but less supportive (it compresses more deeply with the same weight). It can also help with secondary support that “allows” you to sink in more deeply and helps fill in the gaps in the sleeping profile. Firmer materials are more supportive although they may not lead to better alignment which requires a combination of softer and firmer layers in the right proportion to provide the best possible alignment in all your sleeping positions. Too much “support” or firmness or not enough softness and thickness in the comfort layers under the lighter parts of the body can lead to alignment issues just as easily as too little support or firmness under the heavier parts of the body. There is a little more about the relationship between what I call primary support, secondary support, and pressure relief in post #4 here but outside of your own personal testing and experience … mattress design and theory can be a long learning curve with a lot of trial and error because only your own testing or personal experience can know with any certainty what type of layering will match your specific needs and preferences in terms of PPP…
You are in a much firmer range than most people in your weight range would normally choose and I would do some careful and objective testing on different latex designs and layering combinations to see which combinations tend to be more suitable for you in terms of PPP.
I would also make sure you have read the tutorial post here which has all the basic information, steps and guidelines that can help you choose the best mattress including links to some of the pages that have more information about some of the theory and design involved in different mattress constructions although I would only use these as generic guidelines and not as a way to choose the specifics of a mattress because each person can be very different from the next … even if their body type and sleeping positions are similar (see post #2 here).
If you are taking on the “challenge” of designing and building your own mattress it may become more of a project than you are prepared for and post #15 here would be helpful to help you assess the potential risk and rewards and make sure you have realistic expectations about the challenges … and rewards … that can be involved in this approach.
[quote]1. I am considering an online retailer which offers ILD 29, 36, 20, and 32 on their web site. Do you think the following will work? (I will ask if they offer other firmness choices. They will probably provide different firmness for each side as well.)
Top layer (3") ILD 29 for both of us
Bottom layer (2") ILD 36 for both of us[/quote]
I don’t know if it will work for you but it’s certainly outside of the “normal” or “average” range for a mattress design.
It’s not likely that you would bottom out in your sleeping positions (where the layer can’t compress any more) but it may be firmer than you prefer. Don’t forget that thickness and softness work together with other mattress specs to create the feel and performance of a mattress (see post #2 here). This is not much room to “design in” different layers in only 5" and you may do better with a single layer of latex at this thickness. Your own personal testing though is the only way to know for certain,
The tutorial post includes a link to the members of this site that sell latex mattresses online in a wide range of different designs and budget ranges. There are also some sources for individual components and layers listed in post #4 here. some of the better options and possibilities I’m aware of in terms of mattress retailers and manufacturers that are within about 100 miles or so of Detroit are listed in post #2 here.
Phoenix