'Repertoire' is an interesting word. It is used by musicians to mean 'all of the songs or pieces of music that they can play or that they perform'.
Instead of learning linking words or worrying about grammatical structures, it might be better to think about your 'IELTS repertoire'. For example: What topics can you write or speak about with confidence? What band 7 words and phrases are you confident about using?
A large repertoire of ideas, opinions, words and phrases for a wide range of topics is the sign of someone who will probably get a high IELTS score.