Hi Mysterious Penguin,
Unfortunately there is no “formula” that can match someone’s “specs” to a mattress without a reference point of their own testing of specific mattresses except through the averages of other people that may not apply to any individual.
If I was buying a mattress for someone else though … I would probably give them a hand written “certificate” about what I wanted to do rather than the mattress itself so that they could be part of the purchase. IMO … a mattress is too personal, and important, of a purchase to buy for someone else without their own participation. There are just too many variables and “risks” involved with buying for someone else.
As you mentioned … latex is my personal preference for my own mattress (it’s what I sleep on) but someone else may have completely different needs preferences from me and I have no preferences for anyone else … except to help them find the most suitable mattress that has the best possible quality and value no matter what materials or type of mattress they may prefer. I should also mention that there are latex hybrids (with a latex comfort layer and either an innerspring or polyfoam in the support layers) that are in a similar price range to memory foam mattresses (which are also hybrids and have memory foam on top with polyfoam or an innerspring as a support layer).
You can also read a bit more about latex allergies in post #2 here because a typical latex allergy may not apply to a latex mattress.
So rather than giving you specific suggestions based on what I call “theory at a distance”, I can give you some suggestions into the process I would use to make a decision if I was in your shoes.
First … I would make sure your parents were comfortable with memory foam. Like all materials that are unique or even very different from what some people are used to … some may do well with it and like it while other may not do so well and dislike it (perhaps even intensely). The only way to know for sure is for them to try various versions of memory foam mattresses in a showroom. The worst thing possible would be for someone to be given a mattress that either isn’t suitable for their needs and preferences or that used materials that they didn’t like. This is especially true with memory foam which more than most materials tends to bring out “love it or hate it” types of reactions.
Next I would eliminate the “worst” value choices (which you have already done) and then I would talk with each of the merchants or manufacturers you have listed to get their suggestions about which of the mattresses they make or sell may be most suitable for your parents. This would be based on “averages” using their statistics and information you provided about their circumstances along with your parents experiences and preferences from any local testing they had done. In each case I would narrow the choices down to what you and the merchant together believe is the best choice they have available based on your conversations with each manufacturer. Better manufacturers or merchants (and these are the only ones I would deal with) always have the most knowledge about their own specific mattresses and the materials and components that are in it and they also have the experience and many customers’ experience and feedback to draw on that they can use as a reference point to help you make your choices. There is nobody (including me) that can make better suggestions or provide better guidance than they can about their own mattresses.
Once you have narrowed down your choices down to one at each merchant or manufacturer (based on more in depth conversations with them) … then comes the part that can be both the most difficult but also the most enjoyable which is narrowing down your choices to one. I would also make sure that they were involved in this final selection process because there may be things that are important to them that are unique to each mattress or manufacturer. At this point you will be choosing between fewer mattress and making choices between “good and good” and it’s unlikely that there would be any “bad” choices remaining.
From here, if there is no clear “winner” it’s a matter of a (sometimes painful :)) step by step elimination process that may take into account more subjective or finer details and tradeoffs until your final choice becomes clear. It will feel like you are eliminating some great choices (and you will be) and be lots of second guessing involved but in the end you are only buying one mattress and something that may not be important to anyone else but you or some small difference may end up being be the tipping point. Part of the things that could be important here is the relative value of each mattress, the confidence you have that it is the most suitable choice (again based on your conversations), and the benefits of dealing with each of the merchants or manufacturers you are considering including all the options you have both before and after a purchase (in case your choice turns out not to be as “perfect” as you had hoped). Some of the things that I would take into account that may be more or less important to each person are listed in post #46 here.
While all your choices are good ones … a mattress is too important a purchase IMO to buy for someone else (unless there are unusual circumstances where there is no other option) and I really would make sure they were involved at least to the degree that you knew they were comfortable with your choice of materials and the type of mattress you are considering and ideally participating in the final elimination/selection process to see which one they were most drawn to.
Hope this helps.
Phoenix