Les,
Not sure about your Casper. With all that memory foam, granted, it does have some air channels, but looking at the description, it’s foam layered on foam. They place those air channels in the heat-absorbing foam, but then encase the springs with more foam around the perimeter (read about foam encasement here), creating a heat-retaining “Tub.”
Adding a 3" wool topper or horsehair topper may be a sensible solution to maintain heat neutrality, as it wicks away moisture. Horsehair is the best. The bad part is that quality toppers made from these materials are half to three-quarters the cost of the mattress, although, at the end of the day, they may make you more comfortable. We live in NJ and our townhouse is three stories. Our bedroom is over the garage, which is hot in the summer, and we need a portable air conditioner to get the room cool.
I have tested and still have a Perfectly Snug Smart Topper on the mattress, too. We really did not need it with the wool topper, but I like to tinker and try things so I can offer firsthand experience when suggesting something.
I have to say, the PS is quite impressive. No, it is not like having a full blown air conditioner in your bed. It is a 2" topper with a couple of powerful fans built in that help keep the moisture under the blanket down by circulating the air, and it is surprisingly cold. It also has heat, so in the winter, if you need it, it will warm you up. It does not work like a conventional air conditioner, though.
It is designed to follow your natural sleep cycle. You set the app for your typical sleep time, or just engage the app at sleep time, and set it to what is the equivalent of plus or minus 10 degrees from what the sensors in the topper read as your body temperature. Most folks like to fall asleep cool, and your body naturally begins to lower its temperature, preparing for sleep. As the night progresses and your body adjusts to your sleep cycle, up to the point where your body begins to warm up, preparing you to wake, the PS can be programmed to keep you cooler longer for a better night’s sleep.
It actually works quite well and is easy to use. You place it on your bed as you would any other topper, connect each controllable side cord at the head of the topper, and plug it into a wall outlet.
I know you mentioned various claims made and friends’ opinions regarding cooling and cooler materials. My take on it is this: memory foam is going to be one of the hotter, heat-retaining materials. Latex will be less hot. Natural fibers, horsehair, wool, cotton, etc., will be even less warm, if warm at all. NONE OF THIS MATTERS unless YOU are comfortable. Fabrics and fibers do not cool. They are not air conditioners. As @EuropeanSleep described, the moisture/humidity is what makes you feel the effects of the heat. Circulate air and feel less hot. Circulate cold air (an air conditioner) and feel very cool.
You can buy these magic cooling materials all day long, swaddle yourself in them, drape them on your mattress any way you like. Fifteen minutes later, you are going to be hot. I have written about this a number of times. While certain materials and fabric combinations work to cool you down, it is about wicking the moisture away from your body, and then the air dries that moisture so it does not come back to “attack” you. When you are running, walking, exercising, etc., you perspire, and these magic materials remove the moisture from your body, waiting for the air to dry it off the surface. In the case of cotton and wool, they absorb it into the material. When you are on a mattress, those plastic materials not only do not wick the moisture from your body, and even if they did, it has nowhere to go, except back onto your body.
The Perfectly Snug Topper and others like it circulate the air under the covers to dry the wicked moisture that keeps you hot. Horsehair and wool toppers get that moisture away from your body long enough for it to dissipate through the topper. Cotton sheets in lower thread counts and percale weaves, and of course, linen, do a great job allowing airflow and are moisture-wicking.
We used to have a saying as athletes: leave the ego at the door and just play the game. Here, I would suggest, leave the marketing BS at the door and select those things that actually work. Now, don’t get me wrong, there is science behind those marketed fibers, foams, air channels, and so on, but when it comes to use in a mattress environment, they are way overstated, embellished, and not as effective as in the environment originally designed.
Yes, when you go to a showroom where the temp is set at 68 or 65 degrees, and you touch the mattress cover, it is going to feel cold. In that environment, the mattress has been sitting all day absorbing the cold air in the room. When you get home, you put on a mattress protector, sheets, blankets, perhaps a topper, and at that point, the effect of the cooling is negated. Think about a hot day at the beach. The water is 70-75 degrees, but is 90 outside. For some the water feels like an ice box, as there is a 20 degree temperature difference. If it were 75 degrees outside with the water at 70 - 75, it would not seem as cold.
A little smoke and mirrors there.
And don’t be fooled by marketing that says XYZ’s mattress is 10 degrees cooler, until you read the asterisk fine print, only to find out that the mattress that feels 10 degrees cooler is only cooler than that company’s other hot lava quicksand mattress, not the mattress you have at home that you are sweating to death on.
There are mattress protectors made from wool that are not entirely waterproof but offer a wool barrier between you and the mattress like this one. The ones by Naturepedic, Avocado (made with cornstarch to create the PU barrier) , and Birch are very nice, organic cotton on both sides with a very thin PU layer between that is both breathable and keeps most spills from passing through to the mattress.
Hope this offers a little more insight than what has already been given.
Maverick