[pct-l] How to take measurements for a sleeping bag

[L. Michele Scott]

 Hi all!
I'm a tall and, at this point in time, large woman. I carry my weight differently that some women - mostly in my upper body, not hips.  I'm trying to find a good fit for a sleeping bag, but need to know what to measure. I had someone measure my shoulders and hips, but the numbers seemed to small. I'm 5'11" with broad shoulders. 
Is there a trick to getting the best measurements?
I'd just go in to an REI store and try on bags, but the nearest one is over 2 hours away. :\
Thanks,Michele