U.K. Sleeping Bag
The British/Dutch P58 down bag
U.S Army Modular Sleep System
A military sleeping bag means no red Yosemite Sam sleeping bags.
The P58 bags are down filled and are a great price for a down bag. These come in two sizes, Regular and Long. If you are over 6ft tall look for a Long. Since these are down bags it is recommended that you purchase and use a sleeping bag liner. It will keep your body oils and sweat from affecting the down’s loft. The liners come in a variety of colors from white, to sand, blue and olive.
If you are buying a used down bag from an individual be prepared to treat it with down wash and to spend a weekend re-lofting the bag. Most commercial vendors will have done this already.
Another option is the US ECWS system(DPM bivy rather than Woodland if possible)in whatever combination you need to be comfortable or in combination with the P58 bag.
It gets fairly cold out there and nobody knows how you sleep better than you do. If you are traditionally an “always cold” type, consider picking up an extreme cold sleeping bag. If not, you will probably be perfectly delighted with the standard, common, and cheap USGI intermediate cold mummy bag.
I will specifically caution against the cheap mil-tech sleeping bags that you can frequently find on Ebay for $20-$25. They are copies of the Israeli sleeping bags and while well enough made for the price; are very much summer weight bags. Do not bring one of these.