Hi LNZ.
Welcome to our Mattress Forum. 
It’s always nice to hear that the resources and information we make available on The Mattress Underground have been useful in helping propel your mattress shopping decisions.
Thank you for sharing your mattress story and your stats. I am sorry to hear of your sciatica but I am happy to answer your questions as you move forward in searching for a supportive new mattress.
First off, this post about innersprings vs latex support cores in post #2 may better help you decide between a hybrid or an all-latex bed.
One of the great benefits of latex is that even in the softer versions, it has a higher resilience and is more “supportive” than other foams, and will help support the more recessed areas of your body, such as the lumbar, that need “filling in” and are not in close contact with the firmer support layers underneath. So, in short, no! You do not have to sacrifice the softness/comfort and cradling effect to get the support you need to have a neutral spinal alignment.
Coils sleep cooler than an all-foam mattress as they allow for more airflow on all sides of the mattress than thick foam layers no matter how open-cell or breathable the comfort layers above the springs are. When air can move through a mattress, it traps less heat. This said the layers and components closer to the skin are the largest contributors responsible for the temperature build-up in any mattress. There is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range. Latex itself is quite breathable and the most temperature neutral of all foams (including the new generation of gel foams).
I’d keep in mind that the firmness of a mattress and how much you sink into it can also affect sleeping temperature as well. While it’s also not always possible to track down temperature regulation issues for any particular person on a specific mattress because there are so many variables involved (including your room temperature and humidity, your sheets and bedding and bedclothes, your mattress protector or any mattress pads you are using, and where you are in the “oven to iceberg” range) and some people can sleep warmer on mattresses that most people are generally fine with … there is more about tracking mattress temperature regulation issues potential causes ~ Post #2 here (at least to the degree possible for a specific mattress) and the posts it links to that may be helpful.
You are definitely on the right track and it’s good to see that durability is one of your main criteria for selecting a mattress. Latex is certainly a very durable material but I would keep in mind that generally there are some other factors involved in the durability or useful life of a mattress outside of just the material itself (see post #4 here ) so while it’s not realistic to expect every latex mattress to last 40 years for any specific person and it will depend on the specifics of the mattress, as a group they will certainly be more durable than any other foam materials… There is more about the 3 most important parts of the “value” of a mattress purchase in post #13 here which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on suitability, durability, and all the other parts of your Mattress buying personal value equation that are most important to you (including the price, of course, and the options you have available after purchase if your choice doesn’t turn out as well as you hoped for).
Because latex is so durable and also point elastic (conforms to the shape of the weight on top of it without having a significant effect on the area beside it) and because of its high compression modulus (the rate at which material gets firmer with deeper compression) … for most people it doesn’t normally require edge reinforcement for sleeping even for heavy people. This is particularly true if the support layers are firm enough for the person sleeping on the mattress.
Some design solutions for those where the perimeter support is an issue may include something called a “racetrack” perimeter where the outer few inches of the latex support core is surrounded with a much firmer latex. Which would be a very uncommon construction for latex) Typically “racetracks” are made of polyfoam which is a material prone to breaking down much faster than latex, especially in its lower density version. With latex because of its point elasticity though … those who sit on the very outside edge of the unit (instead of sitting with their body weight more towards the middle of the mattress) or those who sleep with more concentrated weight on the outside few inches of their mattress may find themselves sinking down more than they like even though this isn’t normally an issue when sleeping towards the mattress center.
As you already know, Luma Sleep is one of our Trusted members and I certainly think very highly of them and I believe they compete well with the best in the industry. They are very knowledgeable and skilled in finding a good comfort support match for most sleepers.
Brentwood Home has been discussed a few times in the forum. They tend to be relatively transparent with their mattress components. I would be sure that any mattress you are considering is within the Durability Guidelines. I recall this thread where I identified a few weak links in a specific Brentwood Home model. You may also find this Brentwood Home thread interesting. And, you can do a general forum search with the keyword “Brentwood Home” by clicking here.
I hope the above information helps you as you move forward. Please don’t hesitate to ask any additional questions that you may have.
Phoenix