Hi JBR2022,
You are correct that memory foam is the ‘worst offender’ in this regard; but there are a few misconceptions you may be having here. How much ‘heat’ a mattress gives off is determined by the breathability and porousness of the layers closest to the sleeper. Memory Foam will generally be the least breathable and most insulating of the foam comfort materials, so as you noted temperature can be an issue and you’d want to make sure that you don’t choose something with too much memory foam on top that you sink in too deeply as the more you sink into it the more will sleep hot. 2" memory foam layer will retain less of a sleepers heat than a 4" layer of memory foam in the same IFD (indentation force deflection) Lower IFDs (softer foam) and in thicker layers will cause the sleeper to ‘sink’ in more, and more of the body’s heat is trapped in the cradle that is formed, It’s difficult to quantify with any accuracy the sleeping temperature of a mattress for any particular person because there are too many variables involved including the type of mattress protector and the sheets and bedding that you use. You can read more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that can help choose the types of materials and components that are more temperature neutral. 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.
A larger bed will allow the heat to better dissipate especially if the sleeper switches positions to a slightly different area of the bed giving a chance for the previous area to cool off. Heat retention has more to do with the breathability of the whole sleeping arrangement and the type of materials used that are closer to the skin, the IFD, and the porousness of the layers closest to a sleeper’s body. The same goes for the innerspring…and innerspring support system provides good ventilation and air circulation for the sleep system, and does not ‘give off heat’ – that’s determined, again, by what layers are on this foundation, their breathability, and how much a sleeper ‘sinks in’ to the comfort layers closest to their skin…are you perhaps thinking of ‘thickness’ rather than bed size?
There are a few good ways to alleviate excess heat without getting into replacing layers; A good cotton or wool cover or organic layer of coconut coir on the top layer will allow air to circulate and heat to dissipate. A mattress topper will likewise help if it is made with a breathable material in the top layer. You do not say if you are trying to resolve ‘sleeping hot’ and what materials are in your mattress, but if you can provide a few more details - we can possibly address your issue in more detail.
I hope this helps,
Basilio