Hi brittany,
This would depend on how the firmness of the latex compared to the memory foam in the comfort layer of your mattress (under the quilted memory foam layer) and it could also have unpredictable results because adding any material over a memory foam layer will change the response and firmness of the memory foam underneath it which is temperature sensitive. Memory foam and latex also have a very different “type” of firmness because latex is a fast response material that only responds to compression and memory foam is sensitive to temperature, humidity, and the length of time it is compressed and changes firmness levels depending on circumstances. Memory foam can feel firmer with movement or with changes of position but then will soften when it warms up underneath you so it really doesn’t compare to latex. There are also different types of firmness and softness (see post #15 here). If you haven’t tested a similar combination in person you would basically be going by trial and error. It could certainly work “in theory” but anyone that has tried to design a mattress will tell you that theory often doesn’t match their actual experience. I would also be aware that when you have a layer in a mattress that has developed soft spots or is sagging that a layer on top of it will tend to follow the soft spot or the sag.
I would tend to take a “one step at a time” approach and first try to “level out” the mattress and increase the support under the soft spots and then use your actual experience sleeping on this to decide what the next step should be rather than making two changes at the same time (adding support and adding a new layer inside your mattress) that may have some unpredictable results.
You are dealing with some very complex “theory” when you are trying to design what is basically a new mattress and again your own experience and trial and error would be the only way to know what will end up working best for you.
Brooklyn Bedding sells Talalay latex and Spindle sells synthetic and 100% natural Dunlop that uses a continuous pour method (NOTE ADDED: They now only sell 100% natural not the synthetic). There is more about the different types and blends of latex in post #6 here but which one you prefer would be a matter of budget and your personal preferences based on your actual experience because they are different types of latex that have a different “feel”. Without actual experience on each type of latex and different firmness levels I would base your choice on more detailed conversations with each manufacturer who can tell you more about how their latex feels compares to other types that are available both in terms of firmness levels and overall “feel”. Blended Talalay can certainly make a good choice for those that like a more responsive and resilient type of latex or if you decide that you prefer Dunlop then with your higher weight I would lean towards natural Dunlop more than synthetic unless your budget doesn’t allow it but a knowledgeable supplier is in a better position to guide you about the specific materials they sell.
You would basically be building a DIY mattress and I would read post #15 here before using this as a strategy. Accumulating layers that don’t work for you inside a specific mattress design or using comfort layers for support layers or vice versa can be costly because every layer affects the feel and performance of every other layer in a mattress and comfort layers don’t perform the same function as support layers (which need to be firmer than most people would be comfortable sleeping on directly). It would be a matter of accumulating the “right” layers that will be a good match for you in terms of PPP when they are used in a specific combination with each other.
What you are considering in “redesigning” a memory foam mattress is certainly worth trying but may be more complex or risky than you realize … particularly if one of your memory foam layers is sagging or has developed soft spots.
Phoenix