I've got the Duostrap Neo from Gruv Gear.
After six back surgeries since 2008, I was on the verge of giving up playing live because it was so painful.
The Duostrap evenly distributes the weight to both shoulders, plus gently encourages you to keep the bass in proper position, which translates to less pain at the end of the gig.
I'm not an endorser but I would be without a second thought. It has totally saved my playing career.