Light weight mix I have used
When ever we use "light weight concrete, 16 lbs per 1 1/2 inch sq ft" the mix is 7 1/2 sack portland cement, pea gravel, sand (binder) and splash of soap (makes it slippery in 2 inch line pump) and good old H20. There is no air infusion, I think the term lightweight is a miss expression in that the concrete is mixed with pea gravel rather than larger stones making it less structural. For instance If you were pouring a 4" structural slab you would not use the mix above, you would have a larger aggregate in place of the pea gravel, this is a structural mix. As to weight and heat transfer I suspect gype crete and Light weight concrete are about the same (no science to support this statement from me), I understand the relative weight per 1 1/2 inch is near the same. Cracks and cost are the big differences I see. Each has advantages.
Dan

I agree, if weight is an issue and you can't address that issue with making it thinner, then:

"The thermal conductivity, k, for lightweight concrete is usually between 2.5 and 3.6 Btu per hour per inch thickness per square foot per degree Fahrenheit for oven-dry concretes weighing 80 to 100 Ibs. per cubic foot. The corresponding k value for normal weight concrete is generally between 9.0 and 12.0, depending upon the density of the concrete. "

Also, if you cover it with wood or carpet, that will have so much R value that the concrete won't matter much.

The figure I have heard kicked around is 10-11#/sq foot of 1 1/2" gypcrete.