Would "tha mi fuar" be valid here?
Grammatically – yes. But tha mise fuar here is much more natural, because this sentence is contrasting two persons. The emphatic form mise emphasises that it’s me and not you who is cold.
Chan eil thusa fuar, tha mise fuar is surely the best and most natural expression for contrast and emphasis?
Would "Chan eil thusa fuar, tha mi fuar" or "Chan eil thusa fuar, tha mise fuar" work as well?
I am trying to work out when to use thu or thusa and mi and mise