I have in my hands a new book full of very useful info for coplanan design:
Coplanar waveguide circuits, components and systems, by Rainee N. Simons, Wiley Series in Microwave-ISBN 0-471-16121-7.
It is a good book, including usefull formulas, transitions and other usefull topologies.
You can use HFSS or Coplan library for most of your designs.