Which Goalkeeper should Chelsea go out and sign in the Summer transfer window?

Goalkeeper is a never ending topic for Chelsea football club. Everyone thought this conversation will be silent for a few years once Mendy became number 1 but he now sits at second choice behind Kepa. Although Kepa has been quite good since becoming number 1 again, he still has shown moments that question wether he is good enough to be Chelsea's number 1. Chelsea require a world class keep and Kepa in my opinion is just a good keeper, no more no less.