if warmth is not a factor and you want it to be as thin as possible simply a layer of muslin is often used for thin-lightweight 'summer' quilts-
mountain mist batting has a very thin one- there are also very thin batts marketed for clothing/home dec- they do not have much loft. as for weight- wool is very lightweight but lofty- dream orient is pretty lightweight too=not as 'lofty' as the wool