Elementary Korean / Elementary Korean Workbook
​
You can purchase the workbook as a Kindle edition, if you didn't want to buy the book. Both the textbook and workbook are pretty heavy. I'd also recommend using both the textbook and workbook together, as the workbook has comprehension questions on the dialogues in the texbook etc.
I found Elementary Korean pretty good when I took Korean at my school. Grammar was useful, explained well, and there's a workbook that you can buy with it!
Though I wouldn't vouch for the (sequel) book after that which is Continuing Korean due to the grammar that was explained so poorly and grammar points that seemed really useless when talking to other Koreans. (Even my Korean friend who helped me with it said that some of the grammar points that were in the textbook were useless and most Koreans barely use them)