If you think the books are interesting and useful, I suggest buying them to support the authors and you can buy via Coupang at the link at the end of the article.
쏙쏙 TOPIK 한국어 어휘 고급 50: TOPIKⅡ 고급 필수 어휘 수록
시대고시기획 쏙쏙 한국어 어휘왕 TOPIK 1 초급 단어사전 (마스크제공)
1. Korean grammar in use – Beginner: https://sayhikorean.blogspot.com/2018/10/korean-grammar-in-use-beginner.html
2. Korean grammar in use – Intermediate: https://sayhikorean.blogspot.com/2018/09/korean-grammar-in-use-intermediate.html
3. Korean grammar in use – Advanced: https://sayhikorean.blogspot.com/2018/09/korean-grammar-in-use-advanced_10.html