Hit a local dive / paddling store and try some on. I have an MTI vest that sits about 2" above my belly button when seated. The downside is the wierd zipper placement.

A few things to look for:
1. UV resistance
2. Adjustable shoulders
3. Large arm holes
3. Utility pockets
4. Center entry zipper (much easier to use).

Extrasport, MTI and Lotus all make nice designs.