The question is a bit odd to me - it's kind of like looking for a lighter weight girlfriend, because the brakes in your car are failing. There may be benefits to the lighter girlfriend, but you really oughtta start by fixing the brakes. A bass without a functioning truss rod is just a bad thing, no matter what - unless it's a metal necked Kramer.
Dang! That's 1 hell of an analogy! Even better, if he is married, he's screwed! That bass neck is NEVER gonna straighten out!