Hi dsm918,
Firmness is very subjective and relative to each person’s experience and a mattress that feels too firm to one person may feel too soft to someone else (and vice versa) depending on their body type, sleeping positions, and their individual sensitivity to different firmness and softness levels. When you can’t test a mattress in person and you aren’t familiar with how different types of latex in different firmness levels feels to you then the most effective way to choose the options that have the best chance of success will be a more detailed conversation with SleepEZ who can help “talk you through” the options they have available that would have the best chance of success based on the “averages” of their customers that are similar to you (see mattress firmness/comfort levels in post #2 here). There is also more about the different ways to choose a mattress and the risks involved with each of them in post #2 here.
Latex is the most durable of all the foam materials and will soften and break down much more slowly than most other materials so I would focus on which combination will be the most suitable choice in terms of PPP without taking foam softening into account. If you have personally tested two different mattresses and they are both equally suitable for you then I would lean towards the one that was slightly firmer but this would generally apply in circumstances where you are testing mattresses in person because you won’t know for certain how soft or firm any of the options will feel for you until you sleep on it unless you have some reference points based on local testing on different types of latex mattresses in different firmness levels.
This would be a preference choice not a better or worse choice. There is more about the differences between how they “feel” in post #7 here but again … the most reliable way to know which type of latex you would tend to prefer would be based on your own personal testing and experience.
There may be some latex mattresses that you could test locally that you can use as a reference point for firmness and that may give you the chance to try Dunlop and Talalay and see which one you like better and if you let me know your city or zip code I’d be happy to let you know about any options I’m aware of that are local to you.
Phoenix