and an old army surplus arctic bag which is huge! Looking for something a bit smaller.
Look around and see what the market offers - and dont look at seasons too much! Although 3 season is a good bag to aim for, since it will cover much of the conditions you might face, think how you actually sleep. Do you sleep warm or cold? Under a tarp will be colder than a tent, and as a couple of people have said, a decent mat will be essential. I'd certainly got for self inflating (you can always pack a thin closed cell to put underneath) - much lighter, smaller to pack, and much more comfortable.
If you search by the sort of conditions you'll want to sleep in, and how you cope, its much easier than just Googling '3 season bags' - because not only will you end up with too much choice, but its not perhaps realistic for the conditions. I remember travelling in November, where the outside temp. was about 15 degrees at 2am! On the other hand, North Scotland in late June felt like November at times. So going by season is sometimes misleading. And there is no harm in adding a degree or two to what you think your fine with - good down bags tend to slightly underestimate how warm they can be anyway, but better too warm a bag than too cold.
Certainly go for down bags if you can. Much more packable, much lighter, and just more efficient. Remember, your walking, and so weight and bulk are your enemy. Every single kilo will really be felt, so a smaller pack is a lighter pack, etc
Dont worry too much when people scare you about moisture - you pack any sleeping bag in the same way - preparing for the worst, with a dry bag, treat it carefully, etc. And DWR coatings, etc make them more robust than in the past. Rab and Mountain Equipment will be the two best known brands, which you will find in stores, but Alpkit is always a benchmark for excellent value, and you might find some exotic US bags like TNF, etc. There are some good guides, like this
one, and once you know the market, you can look on Ebay, etc.
You have to be realistic in pricing, and I'd recommend setting up some auto searches for stuff on Ebay, which will alert you to new items, but looking quickly on Piclink (which is a pretty handy site), I found an
ME Dreamcatcher, a
ME Helium (which I'd be in the market for myself if I had the money!) and a
Rab 400. And a
Marmot. You might do well for about £120-50, which is pretty cheap for a down bag, even if you sent it off for a clean. Buy the best you can, its worth every penny.
You can buy synthetic, but its really Mountain Hardware which is at the peak these days (they compact pretty small and light for synthetic), Snugpak being not as warm as promised (my Osprey was never as warm as billed, even though it was supposed to be 4 or even 5 season back in the 90's) and not exactly at the cutting edge any more. People might like them for the whole mil spec thing, but to be honest, you can get better value in synthetic with MH, and get down second hand for the same money.
For mats, have a look at Alpkit for a good baseline - again, a cheap mat will be heavier, more bulky for a certain R level than a more expensive mat. The trick is, as ever, to get to know the market, and then get the most for your money, making sure that the essentials like a mat, sleeping bag, pack and boots are as good as possible. The rest you can sort of economise on.