Aaron Martin could be a good option, forgot about him.
Offtop: I'm a big fan of Sarri since last season and honestly think that he's doing a tremendous job. He's built a worldclass team from Hamsiks and Callejons, it's an achievement itself. And the way Napoli are dissecting oppo's midfields is probably the best I've ever seen, probably more impressive than Cruyff's and Guardiola's teams did.
But I'm afraid that their players are not good enough for City, Napoli's success is a bit misleading.
Martin looks promising.
Sarri would be a great option for us after Pep. Really overachieved with Napoli. I think you are really undervaluing Napoli. Diawara is a great talent, played with zero pressure against Real last season in the CL. Would love him here. Insigne is also very good.