Lamina™ -20F/-29C

The Mountain Hardwear Lamina -20 is an option.

I have this bag. It is extremely warm. I use it if the temp is under 20F.

Mountain Hardware uses the Lamina moniker for a bunch of different bags. They currently have 0f, 15f, -20f etc versions as well as womens versions. I have an older -35°c version which is huge but toasty.

I use a Mountain Hardwear Lamina Spark bag for this weather when sleeping without a tent. These are relatively light and not too expensive.

I think you have a valid concern. The problem is not the danger of dunking your bag in a creek, or getting it rained on, it is night after night of absorbing the moisture evaporating from your body, when there is no opportunity to dry it out. I had this happen to me in Oregon, my down bag completely collapsed and it made for a cold night. After that I bought a Lamina, which is fine but it's not as warm and heavier. If I were buying today, I would probably get a down bag with the Nikwax treated down, which supposedly is moisture resistant. I recently bought a Rab parka treated that way, but haven't really used it in wet conditions yet.

My summer REI bag, which is 30 degrees (close to yours) doesn't have much fluff either. I've never actually expected the bag to have loft, because there's so little down. My winter bag from Mountain hardware does puff up, but there's probably 3x as much down in there and it's better down. I don't think your problem was the bag unless you left it in a compression sack for an extended period of time. Or just washed it and it's all clumped up. I can sleep out in 5C/40F degrees in the Sierra Nevada no problem with my summer bag, so i'm not sure why you had so many problems with all that clothing on. I will say 3R is pretty low, a good mat helps a lot.