How autonomous was Sikkim before 1975 as a protectorate? Did Sikkim have it's own currency? Was it a member of the UN?

Hey! I'm from the South, and I take interest in Indian history. I heard the story of the integration of Sikkim into India in an explainer video and I read articles about it too. These questions were left unanswered to me and I couldn't find any answers in articles on the subject. I hope some of you here can chip in!