Moving away from the Franco Prussian angle - I know that research is a fundamental part of our hobby, and there's nothing better than poring over some good reference photo, illustration or text of the subject you want to depict. So I wanted to give a heads up to a book I purchased recently called Waterloo Relics by the publisher Histoire and Collections.
This book is a little gem, though it's not meant to go into deep detail of events of the said campaign, it does present a great photographic and illustrative reference of many interesting artefacts, uniforms and period paintings of Waterloo. I recommend it to anyone interested in painting the period. Check it out if you have a spare few quid.