Here you will find some resources that I have found helpful as I’ve studied Bulgarian. This post contains affiliate links. If you buy through these links, I may earn a small commission at no extra cost to you. If you know of any other helpful books or any other useful resources, please do let me know.
Books
Complete Bulgarian: Beginner to Intermediate Book and Audio Course (Teach Yourself). You can download the audio for free on the Teach Yourself app (App Store. Google Play).
Colloquial Bulgarian: The Complete Course for Beginners (Routledge). The corresponding audio is available on the Routledge website.
A Practical Bulgarian Grammar. I found this to be a very helpful companion to my lessons.
Step by Step: Bulgarian Language and Culture for Foreigners (A1). This is a great textbook for picking up new vocabulary and grammar. This is definitely better when using it with a teacher.
Step by Step: Bulgarian language and culture for foreigners. Workbook (A1). A companion workbook for the above book.