So far I can’t recommend enough the Writers Digest book “Writing the Breakout Novel Workbook”. Its goal, though not stated as such, is to provide texture to your fiction. It already has helped me to think of my protagonist in ways I hadn’t thought of before, by asking excellent questions and “making” me do exercises around these questions. I don’t have any affiliate status or anything else, just want to help other writers here. Take a look!
Finally a helpful book on constructing the novel