You have a lot of leeway.
Basically any non Shadow, Shimano RDER <10 speeds should work, although I'd personally look for an 8 or 9 speed one.
A "mountain" RDER would allow you to use a larger "Big" cog in back.
At least "some" of the Shadows work backwards, where high is low and low is high.
Do stay away from 4700. Wrong cable pull ratio.