I have 3c with a little bit of 4a and I got the Coppola keratin treatment a month ago. I never flat ironed again after the initial application, I just let it air dry. With the treatment I'm a 3b/3c now. I'm not certain if I will have this done again or not. It is fairly pricey and the results for me are just OK.
For many years I got a curly perm using the large rods to make my curls larger, like you are considering. I loved the way it looked, but over time I noticed it was pretty damaging so I stopped doing it. It also irritated my scalp quite a bit.
Anyway, good luck with whatever you decide to do. Feel free to PM me if you have questions.