If not a suit, they need to do motion capture perhaps.
Godzilla has a soul. I dunno what it is, but it is. I know they would slow down the film, so any performance looked hyper at normal speed, but there was a performer inside and somehow like a muppet, that emoting came through all that rubber.
He is a character, he isn't just animal or just a force of nature striking back at us, there is some intellect going on there we don't understand. He has his purpose. Yes and HE is male. King of the Monsters. No egg laying thank you.
The Japanese have that whole love/hate thing going on with him.
Both Godzilla as hell itself arisen and Godzilla as hero.
They need to keep that element too.