Hi JsMom,
I’m not sure which of their mattresses you purchased but latex in general is the most breathable of all the different foam materials (polyfoam, memory foam, latex foam) but there are many factors that can affect temperature regulation besides just the type of foam in a mattress including the type of cover and quilting, the type of mattress protector you use, your sheets and bedding, and other factors that can have just as big an effect on temperature than the type of foam used in a mattress. There is more about the different factors that combine together to affect sleeping temperature in post #2 here.
Most of the PLB mattresses use blended Talalay with an unquilted stretch cover so how it compares in terms of sleeping temperature would depend on the specifics of your SleepEz mattress and the PLB mattress you were comparing it to. The PLB mattresses also use Talalay GL in the top layer and which includes phase change gel in the latex which will have a slight effect on temperature when you are first going to sleep but it will probably have less effect than some of the other factors involved in sleeping temperature. For example a wool quilted cover can have a bigger effect on temperature regulation.
The softness of a mattress would also depend on the specifics of the mattress and the firmness of the latex and some of the PLB mattresses would probably be firmer than your mattress and some would be softer. SleepEz also has options to change the firmness of the layers in their component mattresses.
It will likely become a little softer over the initial few weeks as it breaks in and as you adjust to a new sleeping surface. There is more about this in post #2 here.
Phoenix