I have never personally used sting, so not sure what their gear is like. Sometimes you might have just received a dud which happens. Sandin they might replace that for you, so perhaps get in touch with them.
In terms of belts, the 10mm and 13mm are pretty heavy duty, and if you've never worn a belt before they might take some getting used to. Tough cowhide leather the same width all the way around. Both the quick release and lever belts use the same leather, with a slightly different stitching pattern. But ultimately they offer the same support just a different mechanism of tightening the belt.
We have got some more neoprene varieties, as well as an Olympic weightlifting belt. It's slightly contoured, made from leather but a little less harsh than the lever & quick release in terms of thickness (7mm). It will still offer great support. However, the quick release and lever varieties will offer the most support if you're into powerlifting moreso than bodybuilding.
The small and medium levers are currently out of stock, we have a shipment arriving end of March for this years Fitness Expo in Melbourne. We have taken about 20 pre orders for them so if you're wanting to secure anything in particular we can do that.
Cheers,