I recently got a tempurpedic 1 week before my son was born, he's 8 months now. When he was born he slept on us for months, so by the time he was actually sleeping in the bed the smell was gone & we are very sensitive to smells. I will note from time to time there is some outgassing from the bottom of the bed that hasn't been aired out as much.
-if u can put the mattress in the sun
-put a layer or more of blankets or towels under the sheets - so the dont bunch up under baby
-air out the mattress as much as possible - with the zip cover off (for the first few weeks I did this whenever we weren't in the bed)
-wash the zip cover often
-un-make the bed, a covered bed will keep it from airing out.
-do not use anything to mask the smell, febreeze, etc... only makes it worse.