Lots of questions … so to take them one at a time
Of the three different types of foam (memory foam, polyfoam, and latex) memory foam as a group is the least breathable and the hottest while latex is the most breathable and the coolest, with polyfoam, the most common type of foam in between the two. It’s also true that any foam can be hotter than say an innerspring mattress that only used an innerspring and more breathable natural fibers (such as wool or horsehair and no foam at all) and that sinking deeper into a mattress can be warmer than sleeping on top of it regardless of material however latex is generally considered to be the coolest of all foams and talalay is generally more breathable than Dunlop. There are many other factors that can cause a mattress to sleep hotter including the use of synthetic materials in a mattress ticking. Natural fibers like wool … either in the quilting or in a mattress pad or topper … will also help to regulate temperature in both directions. Overall though … it would be uncommon for someone to sleep hot on latex and much more common for this to happen on memory foam.
Savvy Rest uses high quality materials in their mattress but as you mention and as I’ve also mentioned in many places around the forum (a search on Savvy Rest will bring up many posts), I also believe that their value is not nearly as good as other manufacturers that use the same quality of materials but sell for much less.
Slim lower weight people tend to fall in one of two camps. Either firmer than normal (because their lower body weight and straighter profile doesn’t create pressure points) or softer than normal (because their lower weight needs softer foam to sink in as much as a heavier person would sink into a firmer foam). It seems from your description that you are in the “firmer” camp and that you prefer the feeling of being “on” the mattress rather than “in” it.
The blended talalay and 100% natural dunlop are the two most common types of latex and would have similar durability but different characteristics. There is more about this here. With a firm core layer for support … then the thickness and firmness of the comfort layer would depend on your height, weight, and sleeping positions and of course your preferences. There are some height/weight guidelines here and some sleeping position guidelines here which are a good starting points for mattress testing which can refine the general guidelines into layering patterns which work best for your specific needs and preferences. Actual testing of matresses with known layers is more accurate though than “theory at a distance” so technical specs should never replace your own personal experience in testing mattresses.
The quilting ticking combination can have a significant effect on the mattress. There is more information about some of the choices and tradeoffs involved in the ticking here and in the quilting here. Bear in mind that the benefits of a wool layer can also be added as a mattress pad so if it compresses it can be more easily changed than if there is a thicker wool layer in the mattress quilting … but without wool in the quilting used as a fire retardent then an alternative fire retardant needs to be used (often a viscose/silica fabric like visil or milliken). My choice would probably be either a bamboo/cotton fabric (because of it’s feel and ability to wick moisture and breathability) or cotton (similar reasons) and a knit would be my preference over a woven fabric because of its ability to better conform to a mattress. The choice between a wool quilting or just a stretch fabric with no quilting would be up to the individual and which of the tradeoffs involved were most important in their preferences.
This seems reasonable with a 6" core (of either one or two layers) and a 2-3" comfort layer.
Different sizes will have a significant impact on the price of your mattress but if you are talking about a queen then your lower budget would give you some good choices.
I think you are right on track. While I never make final choices for anyone because there are too many subjective considerations in each person’s value equation … I do my best to help people make sure that all their choices are good ones. Normally the best quality and value is found by purchasing from a local factory direct manufacturer or local sleep shop that carries smaller local or independent brands that they have a good relationship with. The members of this site would be my first choice if any of them are near you however there are other manufacturers and outlets across the country that offer similar value and that I also think highly of that are not yet members. If there are no factory direct outlets in your area which offer good value, then a purchase from an online manufacturer such as the members of this site who specialize in giving guidance over the phone and shipping across the country makes a lot of sense. They are listed with a brief description of what they offer in post #21 here. If you let me know where you live … I’d be happy to let you know of any factory direct manufacturers or better outlets I know of in your area.
There would be little if any difference in durability (assuming the materials are the same) but of course there would be a difference in design and how the mattress responded to an individual (basically multiple layers with progressive firmness allow a layering design to start off softer and then get firmer faster than a single layer of the same material). One is not “better” than another … just different.There would also be a difference in the exchange possibilities with more layers.
Hopefully I’ve answered your questions but if I’ve missed something … feel free to keep your questions coming.