I use this, and like it. It's got two pads to vary the height. I've got a Basset low Picatinny with a 40mm scope.
https://www.amazon.com/gp/product/B0084GS47S/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B0084GS47S/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1