It may depend on the reason you're a mouth breather during the day. Allergies? Deviated septum? Habit? etc. If there is a physical reason why you don't naturally breathe through your nose, you won't be as likely to overcome that just using CPAP. Now, if you have allergies that cause swelling and congestion, using one of the fine filters and breathing filtered air could theoretically reduce the swelling. If it is a deviated septum or other obstruction, you would have to decide if using a nasal pillows mask is worth having repair work done. If it is a surgery you would need, you could search the forum for previous discussions or post a new question here. That topic seems to get quite a few responses.