We have a Tempurpedic King and love it. I have been concerned about the outgassing, but have not been able to find out anything, but wonder if it may possibly dissipate along with the initial smell?
As far as the fear of it over-conforming to the baby, there is a really simple solution. Tempurpedic tells you not to use any sort of mattress pad other than the one that comes with the mattress, as it will interfere with teh conformability of the mattress.
So, if you just put some mattress-pad like material under the area(s) where the baby sleeps, it will not conform as much and will feel more like a firm mattress. This will also protect the mattress against any diaper leakage, which is bound to happen at some point.
For our new baby, I am thinking of getting a sheepskin, and placing it under the baby on the bed.. That will alleviate some of my outgassing fears by taking the baby out of contact with the foam and also will provide leak control.
We really do love the comfort of our bed though. We had a standard mattress when DS was born that was KILLING my back. Then we got a Queen tempurpedic - but traded it in for a King, which I cannot recommend highly enough.
Oh yes, one more thing. My homeopathic MD recommends getting a RUBBER bed instead. I lay down on one in her office and it felt pretty good. But they are even more expensive.