Hard part about your search is that life jackets only function by displacing water. To pass Coast Guard certifications they need to provide a certain amount of buoyancy, dependent upon the certified weight. Non-inflatable jackets generally use foam as the buoyancy material. Therefore all non-inflatable jackets of a certain weight rating will have almost identical volumes.
If you're looking to store jackets away, the only significant difference will be how the foam is broken up into sections. Look for vests that promote flexibility (fishing vests etc,). They'll likely be able to give you more folding options.
You won't likely find vests that take up significantly less space.
Good luck!