This can almost be completed without any searching as most can be found just by moving through the story and coming across them so that you can progress. I say most because there is one (only one) that can be missed.
During Level 3, there is a point where once you have freed the house, a new path will open to the left. If you go forward towards the movable rock you will progress the game and not reach this. So, follow the path to the left.
If this is your first time through this level, you'll come across a memento, which should assure you that this is the right path to take. Keep following this path from the memento (or in my case, just keep looking for merit badge coins) and you'll come to a spot where you'll have to float back to the original point.
If you've gotten this one, the achievement will pop during Level 7 (at least it did for me). Otherwise, return to Level 3 and go find it.