1.’Indian Economy’ by Ramesh Singh:
The book, ‘Indian Economy’ is examination oriented book and covers the entire syllabus/all important topics of Indian Economy for UPSC in very simple language. Along with notes, it also contains practice material that enables students to prepare effectively.
NCERT books are very important books as these books contain all basic concepts required for developing basic understanding for UPSC. These are in very easy and interesting language, so number of books doesn’t matter. Also go through How to read NCERT books.