Hi thelmap,
Welcome to the Mattress Forum! 
Because each person is different in terms of their physiology, weight distribution, and body shape as well as the positions they sleep in, their individual preferences, and the specifics of any back issues they may experience, there is no such thing as a mattress that is “better for backs” in general because a mattress that is good for one person’s back (or back issues) may be completely unsuitable for someone else to sleep on, even if their body type, sleeping positions, or back issues appear to be fairly similar. There is only a mattress that keeps you in good alignment which would be best for YOUR back.
In general, what you would be looking for is a mattress with firm enough deep support and then comfort layers that are “just enough” in terms of thickness and softness to “fill in” and support the more recessed parts of your sleeping profile and relieve pressure in your most pressure prone sleeping position (usually side sleeping for those who sleep in this position) so that there is less risk to alignment in your other sleeping positions.
Latex is a popular component to use in a mattress for those with and without back pain due to the durability and comfort it provides, and there is more about the different types and blends of latex in post #6 here but in general terms all latex is a durable material relative to other types of foam so the choice between different types and blends of latex is more of a preference choice than a better/worse" choice as well. There is more about the differences between Dunlop and Talalay in post #7 here but the best way to decide which type of latex you prefer would be based on your own testing or personal experience.
I would keep in mind that the design of a mattress and how well it matches your unique needs and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) is always much more important than the types of materials and components that are inside it or the type of mattress you choose. Each mattress category includes hundreds or even thousands of different mattresses and there may be several mattresses in each category that are a perfect “match” for you or any particular person, and there will be many others in each category that may completely unsuitable for you to sleep on.
I would advise you to start your research by reading through the mattress shopping tutorial, and two of the more important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to buy a suitable mattress that is the best “match” in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for that are involved in each of them and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful comparisons between mattresses in terms of suitability, durability, and value.
There is also some information about the many different symptoms that people may experience on a mattress and some of the most common causes behind them in post #2 here that may be helpful but the most common reason for lower back pain is a mattress that has comfort layers that are too thick/soft or a support core that is too soft.
The “short” version of all of this is that if you follow the steps in the tutorial one at a time you will have the best chance of success and one of the most effective “shortcuts” that can help cut through much of the confusion when you are buying a mattress is to focus on finding and dealing with knowledgeable and experienced retailers and/or manufacturers that have your best interests at heart (and aren’t just interested in selling you anything that they can convince you to buy). These are the ones that already know what you would otherwise need to learn (including the information in many of the links I listed) and understand the importance of choosing a mattress that is a good “match” for you and knowing what is inside any mattress that you are considering. They can provide you with the type of information and guidance that can help you make the best possible choice. Who you choose to deal with can be one of the most important parts of a successful mattress purchase.
I hope that information is helpful to you. I’ll do my best to answer other specific questions for you once you’ve had a chance to read through the information I’ve provided.
Phoenix
PS – I deleted your other post which was basically a repeat of this one for ease of people following this topic and for the sake of reference to replies.