Planet Waves 50DARE000 Dare Strap Double Strap | Sam Ash Music 1-800-4-SAMASH Slider Straps Dual Shoulder Strap: Shop Accessories & Other Musical Instruments | Musician's Friend
I have not tried the strap shown in the first link. I used the slider strap (second link) for a few months. It helped with back pain, neck strain, etc., but it positioned the bass a little too far from where I prefer to hold it, making my right hand position (picking hand) uncomfortable.
I ended up just buying a high quality, heavily padded, thick leather 4" strap. It seems to do the trick. It's very similar to the Neotech strap walldaja mentioned, but hand-tooled, better looking and, of course, more expensive than the Neotech version.
A cheap, thin, unpadded strap, that is probably the worst thing you could use.