That is a big temperature range.
A couple of years ago I decided to upgrade my 30+ yr old sleeping bag. Just went to the local sporting goods store and picked on a "compact" one that seemed about right. It is a Field and Stream, but I don't see the model. Only had it out a couple of times, but it seemed fine, with a lot less weight and bulk to pack around.
One thing you can do to extend the temperature range of your bag is to wear your clothes on the really cold nights.