It has got nothing to do with being comfortable or not. I was very comfortable with reading all these standard books, but still read the NCERT Text books.
The reason for this is that NCERT books contain the bare minimum information that you need to know for this exam. The standard books are big and very often you miss out on small details. Or sometimes, they don’t have the small details. UPSC often tests you for these basics instead of the rocket science that you might have learnt from these books.
Imagine yourself being able to answer a question about Remote Sensing technology of NASA while not being able to answer a simple question about Kashmiri Pashmina Shawl or Shahtoosh textiles? Why do you want to end up in such a situation? MArks, irrespective of whether you score it for an easy question or difficult question remain the same.
So stop being lazy and read those NCERT text books.