I was thinking of a primaloft 1 underquilt as cheap as you can go.
Spray on glue (good for plastic and fabric) sprayed onto mylar sheet emergency blanket folded over. All edges extend 2-3 in past the primaloft and are glued together except for the bottom end (This will allow air to escape for some breath-ability and compress-ability) The extended edges will be secured with ...
wait for it....
"GRIP CLIPS "
directly to the hammock material. (this will make compression impossible)
Inside the hammock I use my thermarest ridgerest (no moisture can pass through that foam anyway)
I can not think of a lighter option without down.
The grip clip idea will let the sheet be used as an over quilt that does not shift / an under quilt / or turned sideways with shorter ends clipped to each other it forms a tube.