I love this book too! The Shattered World by Michael Reaves. Without a doubt.
A thousand years ago, the world was broken in a great cataclysm; now people live on the fragments, flying between them in ships made of the skin & bone of dragons. The book follows the interweaving stories of a thief, a couple of wizards, and various others as events are set in motion that will take them on perilous journeys to the far reaches of the world with far-reaching consequences.
Matching details from my memory:
- Floating land masses in breathable space
- Werebear/lycanthrope/shape changer thief.
- Sexy deadly woman wizard antagonist
- Botched jewel heist
But honestly, you must not have gotten too deep into the book because the best parts you don't mention, nor will I because of spoilers.
And it was 1985, not the 70s!