Consider using a Climashield Apex synthetic quilt with an adjustable foot box over your down bag such as the one I use from MLD. Weighs less than a 16 oz.. Or you can easily make one from a Thru-hiker kit. There are many other manufacturers offering down or synthetic quilts.
My MLD 48*F/9*C Apex quilt alone handles moderate conditions in warmer more humid climates or zones It is also easily washed and dried. Combined with your 32*F/0*C bag it should yield a possible low temperature of 5*F/minus 15*C depending on your shelter and the clothing worn inside the bag/quilt combination. I like the flexibility of these options.