Hi FelixChi,
Welcome to the Mattress Forum! 
I’m sorry to hear that your back is hurting and finding a new mattress has been difficult for you.
Unfortunately, I can’t begin to diagnose nor recommend what might be causing your back issues, nor would I be able with any accuracy to be able to state what would work well for you, as there are entirely too many personal variables involved, including you existing level of health, flexibility, strength, somatotype, sensitivity, learned alignment from your old mattress, BMI and a myriad of other variables that are specific to you that would preclude me with coming up with any one specific item or style of component that I could be certain that would address your issue. However, with that being said, based upon some of the comments you’ve provided and some of the testing that you’ve already done, I may be able to help guide you in a specific direction, which I hope will be useful.
As far as “hurting” your lower back, a common issue with this is a mattress that does not meet your specific needs for either deep support/alignment, or one that is too plush in the upper comfort layers, or perhaps a combination of both. There is 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 to read about.
Firmness ratings that mattress companies use like “medium or luxury firm” aren’t the most accurate way to describe a mattress, as different companies can rate their mattresses differently from other companies, and comfort overall is quite subjective and the same item can be “rated” quite differently by different consumers. Overall, the only reliable way to know for certain how two mattresses would compare for you in terms of how they “feel” or in terms of firmness or PPP (Posture and alignment, Pressure relief, and your Personal preferences), regardless of anyone else’s opinions of how they compare, which may be different from your own, would be based on your own careful testing or actual sleeping experience on both of them, and in the end that is what I would trust the most.
You state that you don’t like to sink in too deeply, and that you’ve had issues in the past with memory foam and beds where you can feel yourself sinking in too deeply, and this would make sense with what you’ve described and experienced with your low back pains. So even if you tried a product that used higher quality and durable materials, if the surface comfort was too plush for your specific needs, it would still be an item that was inappropriate for what you desired. And while all of the layers of a mattress work together to create comfort, based upon your comments it may be that you desire to avoid something using too much memory foam, or any memory foam at all, in the upper comfort layer, as all memory foam is generally a quite plush material.
You tried something with latex, but you weren’t specific with the complete nature of the product, but if the latex was softer in the upper comfort layer, it could again be that this item was too plush of a surface comfort for your needs. Again, without knowing the complete structure of the mattress, I can only provide general comments, but the good news is that if you do desire something using latex foam, latex is produced in plushness ranges (ILDs) from very soft to very firm, unlike memory foam, which is all quite soft (lower ILDs).
You state that you tend to sleep well on hotel mattresses. In general, “contract bedding” used in the hospitality industry tends to be innerspring in nature, with fewer and harder comfort layers being used, usually polyfoam. Then different “top of bed” products are often used to provide a bit of extra comfort. These “top of bed” products are easily laundered and more cost-effective to replace for the hotels, and are a more efficient and cost-effective manner to achieve a bit of extra plushness than building extra foams in to the mattress itself.
So overall, based upon everything you’ve posted, it may be a good idea to go back to what has worked for you in the past, and seek out a more “traditional” innerspring mattress that uses more basic polyfoams on top, but something that doesn’t use too much foam padding, and what padding it does use is mostly polyfoam and a more medium to higher ILD – avoiding foams that are too plush. You may find these products described as “firm” or “cushion firm” when you visit retailers, but overall only your own personal testing will be able to guide you toward something that is more appropriate and to your liking.
Whatever you choose, make sure that you always find out the information listed here so you can compare the quality of the materials and components to the durability guidelines here to make sure there are no lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress before making any purchase.
Your old Beautyrest would have used pocketed springs for the support unit, so you may wish to consider something using a good strong version of this spring unit, but it wouldn’t be necessary to be a pocketed spring unit. And I don’t know if this is something that you’ve addressed, but I would also consider replacing your foundation, as if it was a Simmons from 8 years ago it would have been a semi-flex wire grid network, and over that time it is common for that style of product to take a bit of a set in certain areas. Also, make sure that the center support in your bed frame is still in tact.
And just to be sure, although it sounds as if you may have already read it, be sure to reference the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
I think you already have a pretty good idea of the “type” of product that works well for you, but now it would come down to finding this style of product that uses better quality materials so that you can expect a decent and consistent comfort life out of the product.
If you try something out and have questions about it, feel free to post any specifics about the product or your experience when testing it out, and I’ll do my best to be more specific in my commentary.
I hope all of that helps!
Phoenix