Huzefa is a serious ultra-lighter, so don't worry if you find his list is a bit out of your comfort zone.
I can't recommend any European brands of sleeping bag because I'm not familiar with them (I live in Australia). However, if you're looking at a quality lightweight sleeping bag the "main"/best US brands IMO are: Western Mountaineering, Montbell, Marmot and Feathered Friends.
You could either buy a 0-5F bag (around -15C) or you could buy a 15-20F bag (around -8C) and wear extra clothes (such as your down jacket) when you need it. Obviously the 15-20F bag will be cheaper, and will probably be more useful on future trips if you don't experience such cold temperatures very often. It would also be lighter that way to. I would avoid buying any bag rated at more than 20F for this trip.
In the 15-20F range, I would consider:
* any bag from Western Mountaineering (ultralite, apache etc... see their website for details)
* Marmot Helium (15F)
* Montbell SS UL down hugger #1 (15F)
If you want more warmth (cold sleeper, or don't want to wear down jacket etc to bed) then look at a WM versalite (10F), WM antelope (5F), a Marmot lithium (0F), or a Montbell UL SS down hugger #0 (0F).
You can't really go too wrong if you choose a bag from one of those companies with 800 fill power down. They all weigh in the range 0.8-1.2kg. If you want a cheaper (but heavier), very warm bag then consider the Marmot Never Summer (0F but weighs 1.6kg)... I've tried one and it is a great bag, super comfy, just a bit heavier.
My ideal bag for that trip would probably be a Western Mountaineering Versalite (10F)... plus a bit of extra clothing if/when needed.
If you don't have access to any of those brands near you, and you don't want to order over the internet without seeing them first hand then you might need to seek advice from some European BPL members. Since I'm in Australia I generally just do a lot of reading and buy stuff from the US. If you want opinions on particular products, and whether they might be suitable for you, the folks here are always very happy to give you their advice.