Hi Cristo,
The process for choosing a mattress when you have back issues or pain is the same as choosing a mattress for someone that doesn’t have any specific issues because in both cases the most important part of a mattress purchase is that a mattress is a good match for your body type, sleeping positions, and personal preferences in terms of PPP (posture and alignment, Pressure relief, and Personal preferences).
There is no specific type of mattress or material that is good for back pain in general because the design of the mattress is always more important than the type of materials that are inside it.
There is more about the most important parts of the “value” of a mattress purchase in post #13 here that can help you make more meaningful comparisons between mattresses.
As you probably know I think very highly of The Mattress and Sleep Company and they are also an invited member of this site. They are exceptionally knowledgeable and helpful and carry some very high quality mattresses and many of them such as the Sleeptek and the Green Sleep can also be customized for your specific needs and preferences as well which can make a big difference in how well a mattress works for you if you are in a situation that finding a suitable mattress is more challenging. I also like the Berkeley Ergonomics mattresses that they carry. They will certainly give you some good guidance and you will be in very good hands when you visit them.
Phoenix