I reckon you're going down a rabbit hole here Dan, you might spend a lot of money and wait a long time and still find it doesn't feel right (neck dive, different feel/sound etc). I injured my back a few years back lifting timber and had to wear a lumbar brace for a gig, amazing how it reduced the perceived weight of the basses (one of which was a lump). I wouldn't choose to do it all the time but it made me realise that there's a lot more to the perceived weight of the bass than the actual weight of the bass (my physio said the brace also altered my posture for the better which would have made a difference also). Have you tried alternatives, wider/heavier strap etc?