Another Western Mountaineering Ultralite fan here. It does have a full-length zipper, so I can ventilate or use it as a quilt on warm nights. Most nights in the Rockies or the high Cascades aren't that warm, at least not by 2 am!

I learned as a child to take the sleeping bag with me when I turn over. I therefore could not use the Big Agnes setup--I'd end up with the sleeping pad on top!

If your budget won't run to a high-end sleeping bag, there's always the Campmor 20* down bag, which is more like a 30* bag, I'm told, but is easy on the budget and not too heavy. Start saving up for a Western Mountaineering or similar bag (top-of-the-line Marmot or Montbell, Feathered Friends), though; they're well worth it! (Watch for full-length zipper models!) Watch also for sales and percent-off coupons. REI does not carry WM bags. WM bags are rarely on sale but some firms retail them for less than others. Keep checking the TLB sponsors listed in the left column of this forum page. These are all reliable firms.

For any sleeping bag, be sure to check your girth measurements (over your insulating clothing and your arms) against the girth specs for the sleeping bag. If the bag is too tight, you'll get that straight-jacket feeling, you'll compress the insulation and will be less warm. If it's too big around, you'll have a lot of extra dead air space to warm up, which takes a lot of extra body heat on cold nights.