@Honch , thanks for the thoughtfulness in your posts. Thanks everyone, actually - lots of great suggestions here. I agree that the bass isn't the issue. Truth be told, I think I'm just looking to justify yet another bass purchase. I already own several basses that are lighter than some of the basses suggested in this thread. Was hoping someone was going to post a bass I never saw before, loved, had to have, that weighed 4 lbs

. I also have a 20% off coupon that's burning a hole through my email pocket....
Believe it or not @Honch , I have those sneakers! Bought them a while back when another company (Sketchers?) was putting out an identical product. Ultimately, they looked too ridiculous for me to continue wearing. I was literally getting laughed at, no joke, and while I didn't care terribly I thought maybe it wasn't the greatest idea. The band also is image conscious, so sitting, strange straps, and strange looking basses really isn't going to cut it.
All the other stuff is completely on the money. My back isn't hurting because of my bass playing, but 6 - 12 hours a week jumping around with a bass on certainly isn't helping. I'm sure it's the things I've been doing in the gym. I've pin-pointed a few of them (calf machines definitely being one), and adjusted my workouts accordingly. I went for physical therapy a few times, but need to find a place that will be more helpful. I learned a bunch of core training exercises that zero in where my back hurts. They know what's wrong, and that makes me happy as there is definitely room for recovery. Just need to find the time to do what I need to do, and stay committed to it.
Thanks again to everyone. This thread got much better response than I thought it would.