Thanks for your advice every one. I think I'll probably try a few layers to give my bob a lift

Have a cut above the shoulders otherwise you're hair can get weighed down and looks flatter. A nice bob (or any variation of this cut) could look good or anything with layers to add volume and make you're hair look thicker.

I would suggest a short to medium length to keep most of the fullness at the ends. A side whispy bang section is always nice to ass a little bounce and style at the hairline and around the face. As for layers, I would add a few longer ones about 3" from the ends. This will create lift at the roots providing body and volume while still not appearing too thin on the bottom. For a more personalizes suggestion, I would inclose a photo.

The length should be longer than your chin, and have layers.

You have many options. Here are three hairstyles you could try. A classic updo, curls, or straight.