Fleece Sleeping Bag Liner
Layers are superior for climate control. It is easy to add a layer for extra warmth and just as easy to remove a layer when it gets too hot. Never mind it is much easier to launder a liner, than a thick sleeping bag.
In cooler weather we use a Microfleece sleeping bag liner, which also doubles as a warm blanket by itself.
For sweat control and that first layer of skin contact take a look at this Moisture Wicking Sleeping Bag Liner