@Laurelgs I'm a guy, so not sure how relevant this is but I had the same concern (I'm a bigger guy).  I shopped and looked at the measurements for waist and sternum and was a little worried (I've got a 40" waist).  I got a Gregory Paragon 58 and the measurements on the specs were spot on.  Very comfortable.  I also looked at the Osprey Atmos and tried a few on and they were pretty spot on too.  Hope this helps.