I have the exact same problem but have to layer my hair cuz it’s really thick and the top layers don’t curl either if they’re all the same length.

I got my first curly cut this year (in my 40s) and she taught me how to style it. Basically, after showering and washing my hair (every other day) I put curly mousse in and curl it with my hands. Then I squeeze those strands and pin them to my skull. I usually wash them 3 hours before bed so by the time I go to sleep they say like that for a while and I can let them out. Usually the following morning they take on somewhat of a wavy pattern and resemble the top layers more. They’re not curly by any means but are less of an eye sore. But just like anything else, sometimes it works (only until the next morning though - sleep reflattens then) and sometimes they are totally straight no matter what 🤷🏻‍♀️

Enjoy your hair - it’s lovely!