Hi CTVKath,
Based on your experience and trial and error it seems like the memory foam layer is the main “culprit” in your heat issues. If I was in your shoes I would probably replace just the 1" memory foam layer with Talalay latex (which is very breathable) or if you want a little bit more temperature regulation yet you could use the Talalay GL fast response (which has phase change gel added to it as well). You could always add an additional 2" of latex down the road as an option after you have tried the single layer. Post #4 here includes some of the better sources for latex I’m aware of.
Post #2 here also has more information about some of the many factors that can affect temperature regulation that may also make a difference and give you some further options as well (such as different sheets, mattress protectors, or mattress pads such as wool).
Do you have a waterproof mattress protector on your mattress or just the in balance mattress pad?
Phoenix