This reminds me that I have a light wt fleece sleeping bag liner that was almost but quite warm enough for 8-10C along the MN Ontario border that I'd be willing to sell at a low price.
It is similar to but not identical to the one at http://www.rei.com/product/739503
Let me know if you are interested and I'll get more specifics (weight, volume, features)
Maybe the lightest and definitely the most compressible would be a thin down quilt. But it might have to be MYOG and down is not so cost/weight effective in thin things.
Next might be a PL1 quilt. Thru-hiker sells 1.8 oz PL1 pre-quilted with scrim on both sides. I don't know if that'd be usable without shell material, you could ask Ayce. If not, Momentum shell would not add much volume or wt.