Alpine sleeping bags

Hi there, I've recently been venturing up into the alpine zone with some winter tent camping in the snow and use of alpine huts without heating. I am looking to upgrade my older 3 -4 season sleeping bag which doesn't cut it for these colder trips. The EN "comfort" and "comfort limit" ratings give some guidance as to what might be suitable. I am looking at the Exped 900 Lite, Macpac Epic 800 and Sea to Summit Ap ii as options but wondering if I can get away with something a bit lighter (in the comfort level -4 deg C range) and a bit less bulky wearing extra clothing(down) in the bag as I see that the EN "comfort" rating is for an average woman wearing only a layer of thermal underwear. I anticipate I could be out in temperatures around the minus 10 deg C range. Obviously there is quite a bit of individual variability in terms of temperature requirements, but are there any women out there who regularly spend nights out in the snow or higher altitudes who might be able to give me some advice? As this is quite a pricey investment and you don't get to test run the bag, I want to make sure I get my bag choice right. Thanks