I haven't Read your Work but from what your looking For in your description above I would suggest the Sacred Heart surrounded by a Cage. Maybe a Bird Cage with Angels in the Back ground lifting the cage towards the Heavens.
Again You are the Only one Best qualified to See the Vision of the Cover. Not Knowing the works contain Makes It hard for the Designer.
Your Front Cover Needs to be Something Everyone Thinks they already Know something about to peak their Interests even Further. Poetry is Often a Hard Sale Religious Poetry Can be easier.
I would suggest you Find the single Most Poem that You Feel speaks Clearest the Message you wish to be Relayed If no Message Then your personal Favorite feel every emotion contain within and select the strongest one.
Seek out a Painter who does this and give them your vision of that emotion or message. As you describe It for another who is Qualified moreso than yourself or that You Feel is You'll come to know It is You who must select a current work Photo, Print, Painting, Stick figure, or whatever it may be. Once you get the Vision Set in you Minds Eye you can proceed to commission It or Draw It yourself or Photograph It Yourself. It may Be It is Not an elaborate Image.
Often we second Guess our Vision because One wants to Un responsible for the outcome or the success You must Own the Complete Book or Vision You Must Do what you were commissioned to Do. But you already Knew This from the Start. She is your Baby Its in Your Hands Asking For Help is okay But Whom is It you should Ask the question To or From The Dream Giver has Given you a Dream Your 95% there Do Not Turn around and Give Up on completing the Vision It lies within in you You already are supplied with the Image of that Front Cover as well as all the illustrations including the Back Cover.
GOD Bless You and Yours. One step at a Time, One Day at a Time You have Possessed everything needed from the Moment You Began your Journey. Ask and You Shall receive. No need to farm out the seed unless it is meant to be for another as well as for you and this may take a little time to be reveal unto You.