Hi Vietnow,
Welcome to the Mattress Forum! 
Both the soft and medium use an Airflow memory foam – 2" of 3.7 lb Premium Gel memory foam (not “cool” gel) in the plush and 2" of 5 lb Premium Airflow memory foam in the medium - which has a more open-cell structure that helps this foam to breathe better than previous generations of memory foam, whether or not a liquid gel polymer is added to the foam or not (which would be more of an addition to durability). And even with a different type of foam used on top, you may sleep warmer with a more plush mattress, as all foams are insulators to an extent, and sinking “in” more in a plush mattress can lead to a warmer sleeping environment.
Memory foam overall tends to be the least breathable of all foams, and if you are temperature sensitive it may not be your preference. You can read more about phase change materials in post #9 here and at the end of post #4 here) and you can read more about the various different types of gel foams in post #2 here. In general terms gel foams will tend to have a temporary effect on temperature while you are first going to sleep until temperatures equalize but have less effect on temperature regulation throughout the course of the night.
Overall, the materials, layers, and components of a sleeping system that are closer to your skin will have a bigger effect on airflow, moisture transport, and temperature regulation than materials, layers, and components that are further away from your skin and softer mattresses or foam toppers will tend to be more “insulating” and for some people can sleep warmer than firmer versions of the same material. There is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range.
I’m guessing that you mean the mattress feels warm to you, not hot to the touch, as there are no thermogenic properties within the mattress itself. And if you’re expecting your mattress to be back to room temperature after sleeping in one spot for a few hours and then leaving it for a few minutes, you may be disappointed with any product you choose, as that would be a very fast transfer of temperature. Even my latex mattress will still have some of my heat signature when getting up in the middle of the night.
Regarding being “angry” with Novosbed, or any other manufacturer for that matter, that I don’t understand. I can understand if you’re disappointed if something doesn’t met you comfort preferences, but there will always be an unknown with ordering something online, which is why many manufacturers offer exchange/return policies. And as a consumer it is your responsibility to become aware of those policies before placing your order, and why it is something I always recommend here on the site. Novosbed is incredibly transparent with their 120 night sleep trial, even to the point of creating a graph to help explain the timeframe for return or the ability for ordering a Comfort+ kit (which you can do after 30 days).
It may be that memory foam, in any form, isn’t to your liking, in which case you might want to investigate some other sort of comfort material with your next mattress, or at the very least read through what I linked to earlier and take a look at your sleep environment to see if there is anything you can do to make things more breathable and comfortable for you in the interim.
Phoenix