I've never owned a lightweight, packable sleeping bag, so I'm hoping some of you would be willing to help me decide on one. The bag won't be for extended touring, but more for short biking or hiking excursions. In other words, ultra-lightweight isn't necessary, but it does need to be reasonably light and compressible (just enough to pack and carry on the bike or on my back).

One thing that seems like it'll limit my choices a lot is that I don't think I would want a mummy shape. I'm a stomach sleeper who gets a bit claustrophobic. Semi-rectangular seems like the way to go, but again, I don't know much about sleeping bags.

Here's some specifics on what else I think I'm looking for:
--35 to 40 degree bag (would rarely use it in colder weather than that)
--Full-length zipper. Bonus if the footbed can be unzipped separately
--Less than $150
--Roomy; not constricting

Any suggestions or advice?

Big agnes has rectangular shaped bags in a wide range of temperature ratings.You will need a sleeping pad to go with one though,because they don't have any insullation on the bottom of the bags.

Thanks for the suggestion, but I've looked at the Big Agnes bags and have decided I would rather not go with that type of system. I should have mentioned that in my original post. Sorry.

There's some bags on this page that would seem to match your requirements:
https://www.rei.com/search?cat=8000&cat=8000&cat=4500001_Sleeping+Bags&cat=40003489&seq=21&hist=cat%2C4500001_Sleeping+B ags%3ASleeping+Bags^cat%2C40003489%3AWarm+Weather+%28%2B35+and+Above%29

I just went through this. I just bought my second Big Agnus bag (guess I am a big fan) with the REI coupon and dividend. I went with the Yuma (40 deg down) to go with my Crystal (30 deg). I do more backpacking and the Yuma will save me space and weight in the backpack during the summer months. The two can be combined together for a 10 deg bag. For me I need to add 10 deg to the actuall bag rating, i.e. a 40 deg bag is really a 50 deg bag.

Do you mean Yampa? (Like you, I just went through this and after a lot of thought went with the Yampa: 40F, down, semirectangular... I'm not aware of a Yuma.)

I also use Big Agnes (Fish Hawk 30 and Moon Hill 0), but for the price the Kelty Coromell 25 F at Sunnysports is an excellent buy:

25 F rating, 650 Down, 66" width, full zipper so can use it as blanket, weighs 2 lb. 13 oz., can compress it down to small size, and cost only $80 with free shipping:

https://www.sunnysports.com/Catalog.a...ock&DescSort=0

It does not have a hood, but that can be addressed easily, especial in the mild temperatures you reference.

The Feathered Friends Sandpiper is a 2.1 lb semi-rectangular 850-fil down bag for one or if used with a separately sold zipped-in groundsheet serves as a quilt for two. It can be made in Epic which imparts serious water resistance so it can be safely used under a tarp. FF quality is second to none so it is a bag that you'll be happy with after DECADES of use. A bit more costly than what you're considering, but well worth it.

https://www.featheredfriends.com/Pica...ctangular.html

https://www.featheredfriends.com/Pica...undsheets.html

It is good stuff.. Have a FF bag myself. I'm very glad they last for decades since it cost me one arm and half a leg. Great quality stuff that I'm sure will last as long as me. Mine is a Hummingbird 20 degree.

YMMV, of course. I have a Merlin 30 degree.