Hi bweaver,
As you can read in mattress firmness/comfort levels in post #2 here, there are too many variables and unknowns involved for anyone (including me) to make good mattress choices for someone else based on “theory at a distance”.
As Smuscles mentioned … the choice between memory foam and latex is a personal preference between two materials that feel and respond very differently and the first step would be to decide which of the two you prefer based on your own testing and experiences. Only each person can decide preference issues for themselves. You can also read more about the pros and cons of latex here and the pros and cons of memory foam here.
In terms of making comfort choices … the “best” way is through testing local mattresses that are very similar to an online mattress you are considering in terms of materials and design that you can use as a guideline or approximation. If that isn’t possible either because you aren’t able to find out enough meaningful information about the local mattresses to use them as a guideline or because mattresses with a very similar design aren’t available locally, then the next best way is with a more detailed conversation with the manufacturer who can give you some insights into what others that have a similar body type, sleeping style, and preferences tend to do better with based on “averages” which can also help you make the most suitable choice … as long as you are inside their averages.
If after talking with them you are still uncertain … then choosing a mattress which either has a good return policy with little cost involved or a mattress where you can re-arrange or exchange layers to change your comfort choice after a purchase … also with little cost involved … can also be a good way to lower the risk involved with any online mattress purchase.
The only caution I would provide is that each person may have very different needs, preferences, and perceptions and what works for one may not work well for another so I would avoid the temptation of basing your choice on reviews or other people’s preferences unless you are certain that their personal experiences, preferences, and circumstances are a good match for your own.
Phoenix