The brand of kit or me?
If this were one night, I'd suggest a blizzard bag, but as it's a week the sleep deprivation from trying to kip in a tube of bacofoil would be counterproductive.
http://www.snugpak.com/index.php?MenuID ... ItemID=142Snugpak Micro Chrysalis.
Was the bag of choice for adventure racers and such for yonks until the advent of ultralight down half-bags - so still is the bag of choice for the discerning vegan. Weighs under a kilo, packs tiny (for synthetic), and I've used it in freezing temperatures with additional clothing. Uses tiny foil filaments to reflect your heat. Costs about £50.
Most important thing about s/bag is not which one, but how to use one and what you put underneath it.
How to use them: Think of them like thermos flasks - best if you pre-heat it. Feed yourself up at bedtime and get in nekkid. Shiver for a bit (10-15 minutes), and then dress to sleep and put in a drinks bottle containing hot water. If you're hardcore enough to be using a pyss bottle, there is value in having that in as well. If you wake because of the cold, nibble some food - the coldest period of the night tend to coincide with the lowest metabolic point of the day, which means you're not heating your bag and you lose its effects at the time you need it most.
What to put underneath them: This is vital as conduction to cold earth will cost you. If you have space or room, use a mat. Thermarests or Exped SynMats are probably the warmest and gucci-est, but there's not a lot wrong about a closed cell foam karrimat. My preference is for neither, but Pacific Outdoors Ether thermo 6 as it weighs nowt, packs up tiny and only marginally more expensive than the best karrimat. But, seeing as space, weight and probably cost are issues, you can always do what the mtn marathoners often do: bubblewrap! Cheap, lightweight, compact, can be binned at the end of your trip. Best of all is the kind you use for household insulation as it's also foil covered to reflect heat.
Given the likely conditions and your solo-ness, I'd recommend bivvying - you can get cheap bivvy bags (e.g. Rab survival zone as opposed a £200 goretex jobby - although a synthetic bag is more resilient to damp) and a basha sheet is a good addition as it is lighter and smaller than the lightest tent and a lot more flexible as to where and how you pitch it while providing good protection from rain and wind.
