Thumbs down on the waterproof sleeping bag idea. Like everyone else has said, it's gotta breathe. Here is what I use/used most recently:
https://zpacks.com/products/30f-classic-sleeping-bag Medium, standard, 390 grams.
https://seatosummitusa.com/products/...-extreme-liner 396 grams
https://zpacks.com/products/altaplex-tent For a person less than 6 & ½ foot tall, 437 grams
https://www.thermarest.com/sleeping-...ir-xtherm.html
6.9 R-value, 2.5 inches thick. 566 grams.
An all weather sleep
& shelter system at under 1900 grams...& there is even lighter, more fair weather systems available; I just don't like being cold. The Thermarest would be the easiest place to save weight by swapping it for a
https://klymit.com/products/inertia-...31722981425242 if warmer temps are expected & you are stuck on having a full length pad.
I have the half length
version. ~160 grams or so. It works well. Albeit a bit weird looking.
You could also easily save another 276 grams (10.5 ounces) over the Sea to Summit Reactor liner by switching to a
Rab silk liner. Making both changes (liner & pad) would net you a 1.2 kilo full fair weather sleep/shelter system.
I've used them all. The 30 degree bag just needed leggings, pants & a coat with wool socks to be
comfortable with a Sea to Summit liner when it was 27 degrees & frosty at Yellowstone 12 days ago. With the cuban fiber tent nothing got wet when the rain set in.
I would've brought the 10 degree bag I own, but the overnight lows were to be in the 50's in Provo earlier this week. When I got to Provo, I just slept in the Sea to Summit liner on the Klymit pad & used the bag as a blanket.