Ring help??

I really like the idea of a birthstone ring of my newborns birth stone. I always have liked rings, especially meaningful ones. The first picture is my wedding set, the second picture is one of my options to stack with my wedding set (it will be gold though). Would it look okay together? If I get it, should I put it below all the rings or on top? Or should I just wear it on a different finger? Or should I just get one like the third picture and wear it on my other hand?