Replacing my older ZPacks Bag? (Current version or other hoodless)

2oz of down should help quite a bit.  If you can sew at all or know someone who does, you could buy 3oz of down fill, use a seam ripper on one of the side seams and add the fill to your current bag.  That might be the cheapest way to a warmer bag.

Seeing as how the bag is fairly new (only three years on it, down is good for at least twenty), I see two options.

1. Buy another bag (as you said.) I would check out the Zpacks to see if they have redesigned the footbox, you seem to like the one you have.  I always worked on the assumption that a 20F spread in bags was good. For example I have three: A 40F, a 20F, and a 0F. These seem to all be consistently  rated but are actually 10 degrees cooler than stated…(probably just me. I always needed long johns, knee length wool socks and a down jacket to hit their rating except the 40F bag. this is good to 35F with the above. )
2. If you don’t mind opening up the Zpacks (you said you didn’t use the zipper) and don’t want to store another bag, just overfill the one you have to 14oz. You could have it done or do it your self for a about 1/3 the cost of a new bag. And it would save storage space.

Personally,  I would likely go for the overstuff rather than overlap temp ranges that closely.

It’s worth noting that I wouldn’t be keeping both bags- once I got a satisfactory replacement, I would be selling my old one.

That also factors into my cost calculations as well- assuming that I sell the old bag for somewhere in the $200-250 range, my “new money” outlay for a new bag would be about $170 or so.

As far as adding fill, I’ve definitely considered it, but I’m not terribly handy and live in a small apartment (i.e. not a ton of space to be working with down), so I wouldn’t be super comfortable DIYing it. I could obviously pay someone to do it, but I’m not sure how much that costs.

I know that Zpacks has a new bag in the works, I think the proto name is the azure? Just in case you want to stick with them you might ask about it, I don’t know the details on it. Also NUNATAK makes very high quality custom quilts and bags with a very good reputation and a more accurate temp. rating(in most peoples opinion) I would definitely look at them.

Opinions vary, but Enlightened Equipment checks most of the boxes if you’re looking for a mix of good quality, value, customer service and longstanding reputation.

I’m familiar with Zpacks and EE.   EE are not really heavier for what you get, in the sense that both companies use almost identical lightweight materials and minimalist construction.  The minor exception is that EE insulates the zipper on the Conundrum, where Zpacks does not.   For a given nominal temp rating, EE specs are for greater loft.  If you compare like-for-like in terms of bag dimensions and loft, the weights are very similar.

Given what you’ve said (that you don’t use the zipper), the Feathered Friends Tanager could work. A sewn footbox is more efficient volume-wise than a drawcord footbox (like on the Flicker), so that might account for part of the down fill difference. The Flicker also has a puffy draft collar and has to fill up the overlapping zipper portion, so I would guess the two are of equivalent warmth with their standard fills.

Another option is the Timmer Made False Bottom sleeping bag. Looks interesting.

If you want to overfill your ZPacks bag, Rainy Pass will add down as well as give it a good wash. Not sure what this costs though. Maybe Goose Feet Gear would be willing to add some overfill as well.