Hi eopandabear,
Just in case you haven’t read it yet … the best place to start is the tutorial post here which includes all the basic information, steps, and guidelines that you will find most helpful and links to most of the more important posts on the forum.
Most innerspring mattresses with a wire border rod would be damaged on an adjustable bed but most pocket coil mattresses don’t have a border rod and would be fine. Some other types of innerspring mattresses can also be specially made to work with an adjustable bed and most foam mattresses (polyfoam, memory foam, latex) are also fine. If there is ever any doubt about the suitability of a mattress for an adjustable bed then the manufacturer will be able to confirm whether it can be used on an adjustable.
As you’re probably aware dust mites are normally the biggest issue with allergies and latex makes a good choice in this case. There is more about latex and dust mites in post #2 here.
I would use the testing guidelines in the tutorial post to test for PPP. Other than that I would also make sure that you are able to find out the specifics of every layer in any mattress you are considering so that you can identify all the materials inside it and make sure it doesn’t have any weak links and so you can make meaningful comparisons with other mattresses. Some of the mattresses you are looking at are not “all latex” mattresses and in some cases you may have more polyfoam in the comfort layers than latex (which would be a weak link in the mattress).
This would be a matter of budget (polyfoam or most innersprings are generally less costly than a latex support core) or a matter of preference (some people prefer an innerspring as their support core or prefer a mix of latex and memory foam in their comfort layers).
This is also a preference choice. Both are high quality materials but some people prefer the “feel” of one and some prefer the other. there is more about the different types of latex in post #6 here and post #7 here also has a comparison between how they feel but your own testing is the most reliable way to know which one you prefer.
Some of the better options and possibilities I’m aware of in the Los Angeles area are listed in post #2 here.
No … most floor models will have broken in already so I would work towards getting as close to your ideal in terms of PPP as you possibly can. If two mattresses appear to be close to identical and you can’t decide between them then I would lean towards the firmer of the two. Terms like soft, medium, and firm are subjective and relative to each person so I would go by your own testing and experience not by how a mattress is “rated”.
Phoenix