All our levels can be completed without purchasing lives, coins or boosters. Our developers only release levels after they personally ensure that levels are beatable without the use of purchases. Boosters and coins can give you the extra edge you need to finish a level, but they are entirely optional and are not needed in order to pass any of our levels.
Try and make super candies (4-5 in a row, or combining candies in different ways) to clear hard levels. Combining super candies will also create a new effect that can sometimes clear almost an entire board!