Jeff,It will depend on how your boots fit. As a rule I would say get the thickest you can fit inside your footgear, and still have a proper fit. Snug is good, tight or loose is bad. Never more true than in the mountains. Heat does not seem to be an issue with most people, as the insoles keep your feet drier. Most of the time it is the moisture from sweat that makes our feet un-comfortable,ie cold or clammy.
Be sure to get some and "Break them in" just like you do with your boots. The insoles will have a bit of conforming to do, to your foot and to the boot. I am not trying for more sales but, when I was guiding in Montana I would ALWAYS have extra socks in my pack and at mid-day I would change them out. If I would have had some felt insoles I would have packed an extra pair of them also. DRY FEET ARE HAPPY FEET! Thank you for the question and please ask anymore that you may have.
Chuck