Hi BigManLittleLady,
As I mentioned in another post today … you are facing the classic dilemma of a couple with very different needs and preferences that need to be designed into the same mattress or “sleeping system”.
There are several approaches that can be used to solve these types of challenges but of course which one may be most effective for you depends on your own unique needs and preferences.
One of these approaches involves zoning which increases the support in the middle of the mattress and at the same time allows for the use of softer materials in the lighter wider areas of the body which need to sink in more but may not have enough weight to sink in as far as they need to with a material that is firm enough for the pelvis. This can increase the odds that the same mattress may be suitable for two people with different needs and preferences.
Another approach involves what could be called “vertical zoning” (although it’s not really zoning in the normal sense) which recognizes that people with very different weights will sink into a mattress differently and “come to rest” in different layers in a mattress. For example a mattress could have a top two inches of soft materials, two or 3 inches of a more medium material, and then a much firmer support layer. The lighter person would sink into the top layer and the top part of the medium layer and this could be soft enough for their pressure relief needs. The middle “transition” layer would be partly to add to the pressure relieving qualities of the softer thinner 2" layer and partly be for support (lighter people don’t need the same firmness level to “hold up” their heavier parts). On the other hand the heavier person would mostly “go through” the top 2" layer and use most of the next 3" layer for pressure relief (heavier people generally need thicker firmer comfort layers to achieve the same softness as a lighter person experiences on softer foam) and then the much firmer support layer (that wasn’t being utilized nearly as much by the lighter person) would be their support layer. In other words … different layers in a mattress can perform different functions for different people.
Sometimes just thickness can make a difference because thicker layers can “act” softer so with a slightly thicker mattress you can use firmer layers on top that are more adaptable to a greater range of weights and sleeping positions. See post #14 here for more about layer or mattress thickness.
Another effective approach is a “side to side split” where each side of a mattress is layered differently to take different needs and preferences into account. In effect you would have two different mattresses on each side combined into one cover (or in some cases a different topper on each side of the same mattress) and each side would feel and perform differently. You can read more about this in post #2 here.
A split mattress (most commonly available in a split king which is two twin XL mattresses but can also be made in a split queen by some manufacturers) can also be a good way to accommodate very different needs and preferences although of course the gap in the middle can be an issue for those who prefer to sleep in the same mattress and use the middle of the mattress. There is more about split king mattresses post #8 here and in this topic.
Which of these would work best would depend on the needs and preferences of each couple. Careful testing with both of you on the mattress can tell you whether any of these options would be a good match for both of you but if you are considering an online choice where you can’t test the mattress in person this is where the help and guidance of a knowledgeable and experienced manufacturer or salesperson who knows every detail of the mattresses they make and sell, how they interact with different people and couples, and that has your best interests in mind can be invaluable.
There are many factors which affect temperature regulation and in many cases a combination of factors can be much more effective than any one by itself. Some of these involve the materials that are used (more breathable materials are more temperature regulating), some involve how deeply you sink into a mattress (sinking deeper into foam can be more insulating and firmer more breathable foams that keep you more “on” the mattress than “in” the mattress can play a role in helping to offset this), and some involve the choice of both the ticking/quilting layers of a mattress or choosing mattress protectors, pads, toppers, or bedding that is more breathable or includes phase change materials that can also play a role in regulating temperature. Finally the environment and the person themselves can also play a role (for example certain foods, drinks, or habits can increase sleeping temperature and the heat and humidity levels in the sleeping environment can also play a role). There is more about the many factors that can affect sleeping temperature in post #2 here.
This is one of the challenges of mattress shopping because when anything seems better it is much easier to make quick choices or buy a mattress that feels great in a showroom but won’t feel nearly as good in the longer term. This is why good and specific testing for pressure relief, posture and alignment, and your personal preferences and spending at least 15 minutes completely relaxed on any mattress that you are seriously considering (or testing as a guideline for an online purchase) can be very helpful. One of the most important factors in buying a mattress is the knowledge and skill of the person that is helping you. The more they know the less you have to know to make better choices. This is where local manufacturers and the smaller sleep shops (as well as better online outlets) tend to shine and where you buy a mattress can be just as important as deciding on which mattress to buy.
These systems are primarily a marketing tool used to sell a particular brand of mattress and are not nearly as effective as the help and assistance of someone who has the knowledge and experience that comes with years in the industry. They also don’t take into account the durability of the materials used or the value of the mattress you are considering and they usually “point to” mattresses that are overpriced. Testing mattresses where the layers aren’t known does little to help you know the type of mattress and layering that may be best for you and Sleepy’s and the major manufacturers like Kingsdown are either not able or willing to tell their customers the details of the layers in their mattresses.
There are some guidelines here that may help you avoid most of the traps and pitfalls of mattress shopping and avoiding chain stores and major brands is a good first step in finding better quality and value. There is certainly no need to spend $5000 on a mattress that will work for both of you IMO when there are so many options available that use as high or higher quality materials and have the same or better performance as the higher priced brands.
You mentioned a couple of times my “other” websites so I should probably make it clear that this is the only website that I have. I was a very frequent poster on another forum called “what’s the best mattress” before I developed this website but I haven’t posted there for years (my account was “deactivated” which is a polite term for being banned :)) They were not comfortable with what I was doing, the information I was providing, or the people I was talking with, and were more interested in “dominating” the information part of the mattress industry for their own financial gain.
SleepEz is one of the manufacturing members of this site and like all the members here I think very highly of them and consider them to be among the “best of the best” in the industry. Shawn is one of the most helpful, patient, and hardest working people that I know in this industry. Like all the members here … they provide a discount/bonus of 5% to any of the forum members here who purchase a mattress from them and share and support the goals of this website.
They are also very good at giving guidance that can help their customers make the best possible choices out of the many options they have available based on their height/weight/body shape and sleeping positions and I highly recommend that you call and talk with them about which of their mattresses may be best for your needs and preferences. Local testing on mattresses where you know the materials and layering can also provide some good guidance and can help them help you more effectively.
There are some general guidelines here concerning height, weight, and body shape and some guidelines here about sleeping positions that can be a good starting point. The overview here and the more specific pages that follow will also give you some ideas of the effects of the different ways to put layers together. These are all based more on “averages” though and your own personal testing on local mattresses with known constructions and the guidance of a manufacturer that knows every small detail of their own mattresses and how every component interacts with different people, has a database and feedback from thousands of customers, many of which would be in similar circumstances to you, will always be more accurate and effective than the more general guidelines that I could provide without specific reference points such as a mattress you have tried and liked (and where the layers are known). Of course I’m always happy to make comments on any particular mattress you’ve tried or provide ideas about alternatives that may work for you or the possible effects that various changes in layering and construction may have 
There is a list in post #21 here of the manufacturing members of the site that specialize in online ordering for those that either have more limited local options or who prefer some of the advantages of ordering online. Many of these provide side to side split layering and provide the option of choosing your own layering. There is a wide range of choices there … each with different options, mattress designs, and budget ranges … but all of them make high quality and value mattresses and are among what I consider to be the “best of the best” in the industry in terms of knowledge, service, and value. Whether the same options are available locally would depend on where you lived and what was available locally but some local manufacturers or retailers provide this option as well.
Hope this helps
Phoenix