Suggestions for a Norse Britain culture hybrid

So I am playing as Ivar the Boneless, now Ivar the Great and Terrible. My goal is to form the Empire of Britain with him. And consultant power with his heir.

One of the way I am planning on doing that is to combine cultures. And reform the faith. But I am not sure about which culture I should make a hybrid with.

If I was to go full RP I would choose Irish, as the current heir is bases in Ulster. But i want the most out of the first blending of the cultures.

Any suggestions?