The Bible is the best of books. Read it daily! Read it carefully and prayerfully. These other books will feed your soul as well and they can be found for free on the internet. Many of the best books are. (See the Aneko Books Channel on YouTube)
On Prayer: Power Through Prayer by E.M. Bounds
On Personal holiness:
For Men - The Normal Christian Life by Watchman Nee
For Women - Called Unto Holiness by Ruth Paxson
On Private Devotions: Manna In The Morning by Stephen Olford