Given your interest in setting a step cut tourmaline in the center, I would suggest we focus our search on tourmalines 7x5 to 8x6 mm. in size.
These images depict an emerald cut 8 x 6 mm. gemstone in the center. Diamonds of varying shapes are set on the sides. These diamonds can vary in shape and number. In this instance, the 3 stones are set relatively low.
A wedding band designed to be worn next to the ring would have to be formed to the shape of the ring as depicted in the last image.
Is this a look you are interested in? Which shape of side diamonds do you like?
If you like the look of smaller round brilliant diamonds set in the band these models might appeal to you. 
