Sleeping bag advice needed

I know there are a ton of these, but it seems everyone has their own requirements. I would be grateful if you could advise.

I plan to be sleeping in temperatures around freezing (30F) with just a tarp. I currently have a LaFuma 600 down rated for 40F with a ThermoMax sleeping bag liner. I'm worried about two things: 1) it won't be warm enough and 2) fog and dew in the mornings. I don't expect to sleep outside in heavy rain.

I want something warmer, but still with a small stuff size. The LaFuma is 6x12".

I have a couple questions,
1) It seems I want down for the small size, but is it a really bad idea if there will be heavy dew in the mornings?
2) Do most sleeping bag zippers mate with each other? (It would be a huge plus if I could get a warmer bag, but still be able to join it with my current one.)
3) Should I instead spend my money on a Thermarest sleeping pad? (I currently have a $5 foam pad.)
4) Any sleeping bag recommendations? I'm also in France, if you can recommend a good online/B&M shop.

Thanks so much!

You should probably say what your budget is.

1) Depends on the outer shell. I use a Big Agnes Horsethief bag, the outer shell can take quite a bit of moisture and it just rolls off. Some UL bags, probably not so good.

2) Probably a bit of a crap shoot.

3) A good pad is important, regardless of what bag you're using. I use an air mattress and add a layer of blue foam when I expect cold weather.

4) Western Mountaineering, Marmot. I really like the Big Agnes bags, too, but they aren't as popular in this community.

30F could work if you can wear some clothes in the bag without compressing the insulation. I have a lafuma 30 degree synthetic bag, and I don't trust it to 30 degrees. I haven't seen their down bags, so I'm not sure how well they are rated. The best way to tell is to measure the loft. Lay out the bag and let it loft up. then lay a meter stick across it such that only the weight of the stick is on it. Then measure from this stick to the floor.

This table comes from JacksRBetter, which is a quilt manufacturer. you would need to double the measurements if you're measuring a sleeping bag's double thickness.
Comfort Rating (°F) Loft (inches)
40 1.5
30 2.0
20 2.5
10 3.25
0 4.0

Loft is cumulative, provided it isn't compressed. Anything underneath you is compressed, so a good pad setup is important.

You may be better off spending another $5 for a second foam pad (closed cell foam) or two. Otherwise, you could splurge on a big agnes insulated or a DAM. The big agnes is pretty light and a lot less bulky than another pad, but way more expensive. You may have luck with cutting down one of the CCF pads to torso-size to reduce bulk and weight.

Bag wetness depends on the overall conditions. If you're spending two weeks out in the cold, with no chance to dry out your bag, you could get into trouble. Though down is notoriously bad, no insulation is truly "warm when wet"

I think you should be able to make your 40 degree bag work with some help. Good clothes, pad, and ideally a quality bivy bag would get you to 30 easily. Double check the loft though!

I wouldn't count on any two bags mating up, but you could bring yours to a store to try.

Also, don't believe everything you read on the internet (including this). If you can test your sleep system in your back yard or next to a car full of extra blankets, you'll be much safer.

If you have the same LaFuma 40ºF bag that I have, I'm not sure it would be comfortable even to 40ºF. I have two 40ºF down bags, one by LaFuma and one by Mtn. Hardwear. The Mtn. Hardwear bag is considerably more lofty... even with fluffing in the dryer I'm not impressed by the LaFuma's loft, and seriously doubt I'd use it outdoors by itself below 60ºF. I have used my Mtn. Hardware in a hammock, with a light jacket, down to about 35ºF and been warm as toast. My son took the Mtn Hardwear bag for his bed (his reminder of 'mom' since he doesn't live with me 5 days a week now), and the LaFuma lives on my couch. I might use it as a liner for my 32ºF synthetic bag, but that's about it.

MNS

Does it EVER get to be 60 F and above in AK?

When I was in TX, I bought a 65 F bag that worked great all the time....in Tx. It is a great bag. Basically, two layers of nylon, and no insulation. Very light and cheap, and warm for Texas summers. Different story here in high mountain SLC.