Light sheet option?

I just get a Buzz Lightyear sheet out of the closet. Been thru 3 kids, so I consider it UL now.

I sleep inside my bivy with bag still in stuff sack off to side. If I get cold, I pull my bag on top of me like a blankie or I get in my bag up to waist or higher as needed.

I just bring some lightweight baselayers that I change into and sleep in my bivy to keep the wind off. Works for me out here in Az, even when you get up around 8k+ in the summer. YMMV.

What about a Jagbag silk liner?

They have 2 grades of silk, a lighter fine silk and a heavier, stronger Endura silk. They make all size bag liners, or sheets or custom make what you want in about any color.

The tie-dye looking ones are way cool.

Oh and shipping from New Zealand to US is free!

I don't know what the summer temperatures are where you are hiking, but it can still be in the 90's in Texas after the sun goes down. When that happens I use a Sea 2 Summit egyptian cotton mummy liner. On really hot nights you can spritz it with some water and get evaporative cooling.

Makes a great pillow when not in use.

I use a Weathershield top from JRB.

Not the current model, but the original – made from Driducks material. Footbox is nice! Also, it works for sleeping under the stars too, due to it's wp/b qualities.

They offer a Driducks poncho now for cheap – should work.

I just crawl into my bivy and sleep on top of my sleeping bag if it's warm, though I'm usually at high altitude where it's not a concern. When those chill, early morning hours arrive, then I slip into the bag.