With hot sleeping, weirdly it’s not about cooling—it’s about humidity control.
People who live in humid places understand that it’s not the temp that gets you it’s the heat-index which is how hot it feels based on how damp the air is. Basically, 90 degrees and dry, with a little breeze is way more comfortable than 80 and humid with no air movement.
Many mattresses marketed as “cooling” use gels, synthetic foams, or phase change fabrics that may feel cool at first but trap heat and moisture over time, making you feel clammy, which in turn makes you feel hot.
A better approach is choosing breathable, moisture-wicking materials that let air and moisture move freely. Talalay latex has excellent airflow (dunlop is good as well, albeit to a slightly lesser degree), while cotton and wool help regulate temperature by keeping you dry, and helping to regulate humidity.
If possible, avoid waterproof encasements, or allergy covers, as they can trap humidity and make overheating worse. (Mattress pads with polyester fill can make you sweaty too.)
Also, your bedding plays a huge role—skip down or polyester comforters and opt for lightweight wool or cotton instead. Stick to 100% cotton or linen sheets, which allow for better airflow and moisture dissipation, helping you stay drier and more comfortable throughout the night.
Regardless of materials, softer mattresses are also always a bit warmer than firmer beds (just because more of your body is in the bed), and “hybrids” tend to have better airflow and moisture reduction than solid foams.
Since mattress feel is subjective, the best way to know what works for you is to try different options in a store, if possible. Edge support is also going to feel different with different products and may not be needed, depending on how the mattress supports you. Latex, in general, has good support, pressure reduction, and durability characteristics, so it’s a great place to start your search. The type of springs (if you go the hybrid route), how the cover is made and quilted, how the mattress is assembled, etc…, all matter too, but sometimes it’s better to just feel the beds! Also, I realize that trying a mattress can be difficult, depending on where you are located.
phew. 
Please feel free to give us a call if you have any questions (even if you are not close to the store), and we will be happy to talk to you about your concerns.