Finding the right piece to fit you perfectly is difficult and surely you need all the help you can get when choosing an outfit. So, I thought the first step is finding the right size. What size are you?
If you're lucky enough to fit one size alone, than you should have no problem shopping for clothes in all mainstream stores. If you happen to be between sizes (for example have the torso fit into a size S and the rest of your body fill the size M), than you need to either alter what you buy or go to a tailor. Of course, you can always start making your own clothes.
So here are a few pictures from a book I hold very dear to me (Alison Smith, "The Sewing Book" ) on how to take measurements in order to make clothes:
(source: Smith, Alison (2009): "The Sewing Book", Dorling Kindersley Limited, p. 60-61)
I hope you find this useful !