Hi LVB,
I’m glad you found us before you pulled the trigger on a “one day sale” before you may have known what you were buying 
You were probably referring to the GTA list but for the sake of others who may be reading this thread (or in case the one you read wasn’t this one) the list of better options or possibilities in the general GTA (including Mississauga) area is in post #1 here.
Post #1 here also has a series of steps (and links to information) that will greatly improve your odds of finding the best quality/value and most suitable mattress possible. These steps are the most effective way I know to find your “perfect” mattress.
A few guidelines that may help (but I would use them as general guidelines not as a way to design your mattress).
His higher weight and sleeping positions means that he will need a firmer support layer (either polyfoam, latex, or an innerspring) and probably thicker firmer comfort or transition layers (firmer foam will feel softer to him than to you).
Your “curvy” figure and mainly side sleeping usually also indicates slightly thicker comfort layers but I would also “err” on the side of slightly thinner to better accommodate your stomach sleeping (which is a more risky sleeping position).
There are also different types of layering that could accommodate both of you where transition layers (the layers in the middle) can function more for support for you (with your lighter weight) and more for pressure relief for him (he will sink into them more deeply and the deeper support layers will be his primary support).
I would also focus on more breathable and cooler materials which includes latex comfort layers and natural fibers in the quilting/ticking. Your choice of mattress protector and sheets and bedding can also make a significant difference in how cool you sleep. If you do go with memory foam … I would tend towards more open celled faster responding memory foam (or a good quality gel foam) which is more breathable but memory foam in general will be a little more risky in this way because it is a more insulating material and the lower density memory foams that tend to be more breathable won’t be as durable with your husband’s higher weight.
Again … these are just guidelines though because your own personal testing (especially with some good local guidance) will be a better indicator than any theory (as long as you spend at least 15 minutes on a mattress completely relaxed (like you are in a pre-sleep state) in all your sleeping positions and testing specifically for pressure relief and alignment and any other preferences that are important.
If motion transfer is a bigger issue … then I would tend to avoid 3 of the 4 types of innersprings (pocket coils being the exception) but polyfoam or latex support cores will also work well. There is more about the different material possibilities for both comfort layers and support cores in the overviews that are linked in the previous “step by step” link.
You will basically need to test both the firmness level of the support core (to make sure it keeps you both in alignment) and the firmness level of the comfort and transition layers (which will provide the pressure relief). The two main functions of a mattress are support/spinal alignment and comfort/pressure relief and the deeper layers provide the support and the upper layers provide the comfort/pressure relief.
A pillowtop is just a method of construction (like an extra topper on a mattress that s more loosely attached) and can be used with both good quality and lower quality materials. The reason they are so often an issue is not because of the pillowtop itself but because most of the mainstream mattresses that have them use lower quality polyfoam in the pillowtop that is subject to early softening and breakdown. These same materials would be just as risky with a mattress didn’t have a pillowtop but had thicker layers of lower quality polyfoam in the upper layers no mattter what type of construction it used. The key is always to make sure that the upper layers of your mattress use the most durable materials possible because these tend to be the “weak link” of most mattresses.
Several of the links in the GTA thread are reasonably close to you and if you connect with people that have good knowledge and experience that can help “fit” you to a mattress you may well find that a pre-made mattress will be fine. Some of them can also do custom building (or order a custom build from their factory supplier) so if this is necessary then it would certainly be a good option but it probably won’t be necessary.
It’s always easier to “connect with an expert” than it is to become one yourself or get overly involved with mattress specs or design.
The goal is always to work with an “expert” and let your body tell you which mattress provides you with the pressure relief and alignment you need and the other preferences you want rather than trying to become the expert yourself or design a mattress based on specs. “Just enough” knowledge to help you ask better questions and to be able to know that the person that is helping you has more knowledge than you do is all you really need.
so to recap …
Step 1 is knowing what mattresses and sources to eliminate (major brands and chain stores primarily), some warning signs and pitfalls to avoid, and some of the general things to look for.
Step 2 is some basic research into mattress construction and materials to get a sense of the types of materials you want to consider and test.
Step 3 is researching some of the local manufacturers and retailers by calling some of them that are close to you to make sure they are knowledgeable and experienced and can tell you the details of what is in their mattresses.
Step 4 is to visit the ones that you were most attracted to (from your phone calls) and testing mattresses with their help and guidance that use the materials and styles that you want to test. This is the step people usually do first without the first 3 that should come before it and without the other 3 steps this one can lead to some lower quality/value choices if you look at major brands, spend time in chain stores, or work with someone that doesn’t know what is in their mattresses.
Step 5 is to look at all the tradeoffs between your top few choices and decide which of them best fits your “value equation”. In most cases … by this time all your choices will be good ones and it’s just a matter of picking out the “best” among the “good”.
Phoenix