I have heard many authors advise people to choose a point of view in their writing and go with it. While I agree that you must be clear about who is speaking in your book, I also think it’s okay to mix first and third-person narrative in the same novel.
In the second book of The Durant Trilogy: Seeking Durant, I chose to write the book predominantly in first-person, from the main protagonist’s point of view. However, sprinkled in amongst the chapters in separate chapters of their own are third-person perspective points-of-view. While this may seem strange, the point of doing this is basically to help the story make more sense and to develop the plot and characters more fully.
The main thrust here is, if you need to mix POV, do it. Just make sure you do it in the least confusing way possible and with the purpose of advancing your plot and characters. Sometimes it’s okay to mix it up.