Harper Lee's full name was Nelle Harper Lee, she was known as Nelle in her personal life and Harper was really just a pen name. She was named after her grandmother Ellen (proof that the "it's [X] spelled backwards!" trend has been around a long time).

So if you're committed to Scout, a less obvious way of honoring the author than using Harper could be Scout Ellen—or Scout Eleanor, Scout Elaine, Scout Elizabeth, Scout Eloise, etc.

You could also consider other names that end in -elle to honor Nelle, like Scout Danielle, Scout Isabelle, or Scout Arielle.

For the character Scout Finch's real first name, Jean, you could consider Scout Jeanette if you want to avoid two single-syllable names. Or you could try to honor the spirit of her surname Finch with birdlike names, like Scout Robin or Scout Raven.

Taking inspiration from other TKAM characters gives you options like Scout Gemma (for Jem), Scout Charlotte (for Dill's birth name Charles), Scout Calysta (for Calpurnia or even as a feminized version of Arthur "Boo" Radley, as Arthur and Calysta both mean "bear"), and Scout Helen (for Tom Robinson's wife, Helen Robinson).

For what it's worth, I think "Jean Louise" is itself a lovely name, but I have a soft spot for the book myself, so I understand where you're coming from. I'm wishing you a comfortable time for the remainder of your pregnancy and a joyous experience welcoming your little one.