I think I'd move Darmian inside and see how he gets on.
Read a lot in the summer that he can play at center half so would like to see it. And hey who knows... If he performs well at CB with Varela looking good at right back maybe it helps us for next season?! I'd certainly like to see it given a go as I'm not sure Darmian is the answer long term at right back. Not from an attacking perspective anyway.