Sleeping Bag Length - Some manufacturers make the same sleeping bag in various lengths to suit taller people. Short, Regular and Long bags normally refer to 5'6", 6' and 6'6" respectively - but not always - Yeti for example produce a Medium bag for people up to 5'6".
Obviously you should buy the bag to suit your height. Some manufacturers only make bags in one length, or perhaps two (Regular and Long) so you don't get the choice.
Womens Specific Bags - These are generally made shorter than Mens bags and are a slightly different shape to more closely match a Womens shape. Some Womens specific bags have more down in critical areas such as the feet, which have been proven to be particularly susceptible to cold for a Woman.
Sleeping Bag Girth - Most manufacturers quote the internal girth around the widest part of the bag - at the shoulders, this can give you an idea of how restricted you might feel in a particular bag and is a good comparator between bags. In order to decide about girth you can measure the same dimension on your previous sleeping bag and compare it to the quoted figures. Or you could use a loop of string tied at the appropriate length to gauge how it might feel.
Rectangular versus Mummy shapes - Most sleeping bags you will see on our website are Mummy shaped, this is because a close fitting bag will be warmer for a given weight because there is less volume of air to move around carrying heat away with it, and a close fitting bag weighs less than other shapes because there is no waste of material.
Some people feel too restricted by a mummy bag and would rather carry a bit more weight and have a sleeping bag with lots of room in it. Rectangular or Tapered bags offer the user more room to move around and often the bag completely unzips around the feet so that it can be used as a quilt rather than a sleeping bag. Often tapered bags don't have a hood - as the focus is less on maximum heat for minimum weight, and more on comfort and freedom to move around.
Quilts - This refers to a flat quilted cover that offers complete freedom of movement when sleeping. The danger here is from draughts, and you need a warm sleeping mat to insulate you from the ground.