Bishop Pass 0F/-18C

Dew and mist should not be a problem for you. Soaking is what you need to avoid. That bag has a waterproof finish on the outer shell. It’s likely to be wet from condensation when you wake up but it will dry quickly. I find that when I pack up, to hit trail early, with some moisture on the outside of my down bag, it still dries and relofts quickly when I set up camp.

Just a recommendation, as I was at the same point as you a few years ago. Condensation in the tent, wet bag in the morning, cold nights, etc. Felt like my gear was failing me. Then, while on a longer trip I started using the rain fly while keeping the tent vents fully open. This gave the tent a chance to have some aiflow, which eliminated the condensation inside that was coming from my breathing inside the tent. My sleep system was already plenty warm enough (Closed Cell pad, Inflatable pad, Bishops Pass 0F bag) so I stayed warm despite the new airflow that was wisking away the hot, humid air I was breathing out. Another super important part to avoid condensation is site selection, as ground water evaporation can easily enter your tent and turn it into a tiny little rainforest environment. A tent footprint helps if there aren't good sites with lots of drainage. I would recommend doing some research on this if you haven't considered much on this point in the past. I've camped like this in downpours and sub 0F temps without issue since then and all it took was a change of habit vs new equipment to avoid the wet situation you're talking about.

OP — what temperatures do you intend to most regularly use this bag in? A 0F bag is too warm for anything above 25-30, in my experience.  I’ve used my 0F bag at ~40 and ultimately found that I had to use it as a hot, half ass quilt that weighs 3lb. Moreover, where backpacking is concerned I just don’t think synthetic can be a valid insulator for a bag at that temp.  I use synthetic  to ~40F and down beneath that. That much said, if you’re looking for the most versatile sleep insulator I would get a 20F quilt and save the money.

I really enjoy my mountain hardwear bishop pass. It’s not top of the line though. It’s rated 15* Fahrenheit, 2.5 lbs (just over a kilo), and packs to a decent size (not super small but not huge). For reference I usually backpack in the sierra Nevada range of California. So average nightly temps are around freezing. I would recommend this bag but of course you can get nicer if you have a larger budget. I think the two most important things to consider are nightly temps and material: 1) do you really want a -9*C bag? I’m not sure how cold it really gets where you are but I feel like there is a good chance you are going to be dripping in sweat with that for a lot of nights that aren’t mid winter. 2) synthetic vs natural down. I prefer natural because it’s so fluffy and warm. But both have their pros and cons. Side note: not even sure if mountain hardware is offered in NZ lol

If you're not into making your own synthetic quilt as suggested above, some sleeping bags come in both a right hand zipper and a left hand zipper and can be joined together at the zippers. Looking now I'm seeing fewer options that do this than before. ☹️ For example the Women's and Men's Mountain Hardwear Bishop Pass bags are left and right zipper respectively, but neither the Kelty Cosmic Down 20 nor the REI Magma bags seem to come in alternating zipper sides. Mountain Hardwear Lamina Eco AF comes in both left and right zips. It's a synthetic bag so it's cheaper but will be a bit heavier and take up more space in your pack than a down bag. But so would a MYOG quilt as described elsewhere.

Thats good to know! Thanks I only discovered them recently by accident when I was trying to find a midlayer fjallraven in my size and the quality of that from haglöfs blew me away I ended up getting the mountain hardware bishop bag because of the advertised range being better and the goretex that mountain hardware makes it with. Im canadian and will be using it in the outback which means possible water exposure in the canoe and in the winter; which our winters which i assumed is pretty comparable to your winters which is why I appreciate my fjallraven stuff so much. But I think ill be keeping Haglöfs' bags in mind for when anyone i know is shopping replacements or upgrades

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.