This is a really good write up for the whole gauge switch to LED. Around page 4 or so they get into the HVAC controls.
The push button centers are a 5mm LED; kinda like:
And the remaining ones for the HVAC are a 4mm NeoWedge LED; kinda like:
Hopefully this helps. I am planning on doing this same switch in the next couple of weeks, and I know the pain of doing this research. It has been a pain in the A$$. Good luck.