What do you have now? You might want to consider if you have any latex allergy or are sensitive to dyes etc they put in lots of plastics etc before looking at any of those pads etc.
Natural fiber like cotton is cooler, these days everything is microfiber so people are sleeping in plastic wrap clothing in plastic wrap bedding, it gets much hotter and prevents cooling IMO.
Also, I don't know if you are female or not but if this is new and if you don't mind me asking, are you sure it is the mattress and not you reaching a certain age and making your own heat when your ovaries slow down? That whole thing snuck up on me way earlier than expected. Autoimmune can do it too, consider your health as well.