I spent too many years trying to straighten my naturally wavy hair. I stopped a few years ago and discovered it's curly, not wavy; full-on Regency ringlets!
I spent too much money trying different "miracles" to encourage the curls! I read lots about the CurlyGirl method and tried various things but dismissed a lot as being too much faff.
What I do now (I should add I'm white, I think advice might be quite different if you have Black heritage)
Shampoo it infrequently (barely x1/week, but my hair's always been dry, which is often the case with curly hair) (I use cheap Aldi shampoo! but more expensive conditioner with argan oil when I wash it, and always leave it in for a few minutes before washing it out)
dampen it every day even though I'm not washing it
a smidge of conditioner raked through whilst it's damp, whether I've shampooed it or not (tresemme is good for me at this point- I find some brands too heavy/sticky) (smidge = a blob about the size of a butter bean, rubbed with a bit of water between my palms then raked through)
Wrap it with an ordinary towel to get most of the wetness out, but I don't rub/scrub it with the towel
Brush it with a DENMAN brush before it starts to dry. I only got this a few months ago and it's so much nicer than any previous brushes.
leave it alone until the next day! Even a diffuser makes it frizz so I always air-dry.
You may need to experiment with different conditioners. My hair is thick but quite fine now that I'm post-menopause --what suits my hair is very different from what suits my daughter's much coarser hair.
I've never bothered with silk pillowcases etc.
I don't look very sleek but my goodness, life is easier now I've learned how to manage the curls!