Hi PeterKKB,
Welcome to our Mattress Forum! 
I have moved your post to its own thread as from your description I am guessing that you are looking at some European beds.
Sorry to hear that none of the 4 different mattresses you tried hasn’t worked out for you. You’ve certainly struggled through this and did good work as your current final choice has many “characteristics” of a mattress that sleeps much cooler than a typical memory foam mattress. While I can confirm your findings in terms of material choices … the sleeping temperature of a mattress is determined always by a combination of several interacting factors in combination with a specific person and environment.
There is no standardized testing for temperature regulation with different combinations of materials but all the materials used in your mattress of choice favor breathability, moisture-wicking, and a much cooler sleeping climate. To summarize and add a few other factors to consider:
• You are correct to move away from the memory foam as this is the least breathable foam and can sleep warmer than other materials.
• While the upper layers of a mattress are the most significant part of temperature and moisture regulation … deeper support components that allow more airflow also have an effect and so pocket coils are one of the most breathable types of cores and will also tend to sleep cooler than foam support cores as long as the air can ventilate to the outside of the mattress.
• Latex also is the most breathable and “temperature neutral” of all the different types of foam materials but the firmness of a mattress and how much you sink into it can also affect sleeping temperature as well. Latex allows for more airflow than any other foams and when changing positions on the mattress the air will be moved in and out like within an accordion but this depends also on the order of the layers and components.
• Wool is also a great choice in the comfort layer because of its ability to store moisture and perspiration without feeling wet (it stores moisture inside the fiber itself) and regulates temperature this is also great used in combination with cotton because of its ability to wick moisture away from the body into the wool. Cotton doesn’t, however, store moisture as well as wool without feeling wet.
• I am not aware of any specific mattress that uses “Denim filling” unless you are just referring to a Denim mattress cover that the bed uses. (You may wish to provide a link to the mattress you are asking about … I’d be very interested to see it)
• In very general terms … the layers and components of a sleeping system that are closer to your skin will have a bigger effect on airflow and temperature regulation than layers and components that are further away from your skin and softer mattresses will tend to be more “insulating” and for some people can sleep warmer than firmer mattresses and how they compare would also depend slightly on the order of the layers and components
The temperature microclimate has much to do with your own temperature sensitivity, the materials used in the mattress that are closer to the skin and many other many variables involved (including your room temperature and humidity, your sheets and bedding and bedclothes, the mattress protector or any mattress pads you are using, and also where you are in the “oven to iceberg” range) . Generally, some people can sleep warmer on mattresses that most people are generally fine with but you can read more about tracking mattress temperature regulation issues potential causes ~ Post #2 here (at least to the degree possible for a specific mattress) and the posts it links to that may be helpful.
I’ll be interested to learn about how you progress through your evaluation.
Phoenix