Hi passionate4nature,
Water isn’t harmful to latex but solvents, ultraviolet light (like sunshine), ozone, some heavy metals like copper, and oils and fats can be very harmful. I would avoid any exposure to direct sunlight which can destroy latex. You can use water or very mild detergents or isopropyl alcohol to spot clean it (making sure you use a damp cloth to soak up any detergents or residual cleaning agents) and then let it air dry in low light before re-covering it. You can also sprinkle it with baking soda to help disinfect it and soak up any excess water and then vacuum it off. If you are looking for cleaning all the way through I would vacuum it first. I would then use only cold water and then like a sponge … soak and gently (the foam can tear) press out any excess water several times (or use a piece of dowel or something similar to roll over it carefully) and then soak up as much water as possible with clean absorbent cloths or a chamois so it is as dry as possible and then let it dry indoors away from any direct light sources or any other sources of harmful exposure (such as electrical machinery that produces ozone) until it is dry. Using a fan would speed up the drying process.
I would tend to be cautious with steam cleaning because high heat may further cure the foam and change it’s characteristics. Occasionally would probably be OK but I would not do this on a regular basis and only if the other methods weren’t enough.
Generally the latex itself wouldn’t need to be deep cleaned except with spot applications because it would be covered or protected with a mattress or topper cover or a mattress protector and bedding.
You can read about the durability and aging characteristics of different types of latex in post #2 here. Softer latex (Talalay or Dunlop or any material) is also subject to greater compression and mechanical forces and will soften more than firmer latex (which is also true with other foams as well). You can read more about the different factors involved in durability in post #4 here and the posts it links to.
I don’t know of any consumer sources for just pocket coils although Bay Beds sells component latex/pocket coils mattresses with pocket coils that can be exchanged. You can also buy a used mattress just for the coils and then tear it apart and clean the coils and use them for a DIY construction.
There is some generic guidance in the “putting the layers together” and in the “sleeping style, preferences, and statistics” sections of the site as well as the “tips and tricks” page but there are too many variables involved for me to provide any specific design recommendations because there is no way for me to know how anyone will feel on any material (and especially material combinations) that would be more accurate than your own personal testing and experience and/or more detailed discussions with the providers of the materials or mattresses that you are considering who will have (or should have) much more familiarity with the specifics of what they are selling than I would. You can see more comments about trying to duplicate another mattress in post #4 here and in an my earlier reply today in post #4 here.
Phoenix