Extra mattress pad or Thermarest

[BobWilson]

I noticed in a previous post a while back that some people used Theramrest mattresses.  Do you know which model or at least how thick they are?  Like everything there are options and decisions to make.  
Is 1 1/2" enough, or 2".  I'm sure they would still have to be deflated to close the TM.

Egg-crate mattress pad:  At home one day I tried an egg-crate type foam mattress pad on top of our regular bed mattress and I noticed that it was a lot hotter to sleep on those summer days, so I took it off.  The foam cell seems to act as an insulating barrier.

The Thermarest may be great insulation when it is cold but I wonder if a regular air mattress on top of the regular TM foam mattress would be better when it is a hot night to sleep.

If you put your Thermarests under the TM mattress.  This could be good insulation when it is cold outside to prevent heat loss from inside the TM through the bed support.  

Seems like it would be good to have a different plan for hot days and cold days.  I would still like to have a little thicker mattress than the standard that comes with the TM.  So something would need to be added.

Anyway my main question to those that use them is how thick are your Thermarests?