Hi noracharles89.
Welcome to our mattress forum!
Thank you for sharing some of your DIY journey with us. I am glad you’ve found a great combination of layers that works for you.
As a rule, natural fibers allow for more airflow and humidity control which should translate into better temperature regulation, and natural or more breathable fibers in the ticking such as cotton will wick away moisture and ventilate better. That said, one also has to consider the thickness of the materials in the top layer of the cover. The more closely these materials conform around you, the more insulating it will be. In other words: the deeper you sink … the more body heat is “trapped” under you regardless of the materials used. While taking off the cover may have allowed for more ventilation a down/feather topper or featherbed is more “fluffy” and it will pack down and compress more, which requires more maintenance and regular “fluffing”. They are not great with moisture, they will also tend to be warmer than other materials.
I took a look at the topper you bought and can see it comes in 2- and 3-inch layers. I would suggest looking into covers made with natural materials that aren’t toppers. A number of our Trusted Members sell covers/mattress encasements that don’t come with the additional “bulky” topper component. And are made from new-gen fabrics that help with temperature regulation such as Tencel fibers which absorb moisture into their unique cell structure until it can be evaporated away, but I’d keep in mind that the amount of “cooling” that the cover material would provide would be quite temporary, and you can read more about phase change materials in post #9 here . There is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range. Latex itself is a quite breathable material.
Hoping this is a good starting point and let us know if you have any additional questions.
Phoenix