I had a series of lower back issues and had a few sessions with a sports' injury specialist. He told me about a set of muscles I had never heard about - transverse abdominus (TVA) - that run underneath the front set of ab muscles and wrap around the centre of the body, anchoring into the lower back. He considers these to be one of the most important muscle groups you can exercise, affecting posture and pretty much everything you do, but are largely neglected which can, if you are prone to back issues, lead to problems. Certainly since being made aware of this and doing the exercises until the right posture becomes second nature I have had far fewer problems. It wouldn't hurt to make a few enquiries.
A few weeks ago I bought a Hohner B2A from a fellow Basschatter (Hi Steve) and am currently in evangelical mode about it. It is [i]incredibly[/i] comfortable to wear (with a slight mod to move the front strap button to somewhere sensible) and lightweight. I can hold it up by one finger when it is in it's case at arm's length (engaging the TVA first, of course) which, coupled with the Liliputian proportions, make it so easily portable. But, more importantly, it plays like an absolute dream - a [i]really[/i] comfy, fast neck. And the active preamp give a great growly tone - it certainly punches way above it's weight. Aesthetically you love 'em or hate 'em - personally I think the economy of the design is actually effortlessly cool and will seek out the Hohner G3T (6 string equivalent) for when I want to noodle about with such a thing.