I've had one idea for the book covers for a while now--originally it was the idea I had for the combined single book, but when it split into two so did the cover concept. Neat how that worked.
About a week ago, I had another and have been living with that as a second option. Still like it.
And this morning woke with another one.
So I think I can start sketching them now. Each idea is a set of covers, visually relating the two separate books.