38mm is way too big unless you have really long hair. even 32mm can be a lil big for short hair.
I have a 32mm babyliss pro. i don't think u need to straighten your hair first. those waves in the picture are relaxed already. after curling, you need to apply products and separate the curls with your finger. Unless you just wait for it to drop.
even with 32m,, my curls are way bigger than those and looks much more natural...if you look at the top of her head, u can see lots of dry brittle hair..looks damaged from heat.
If you plan to curl your hair every day then it's probably better off getting a digital perm, your hair will look like that all the time. Go to a japanese or korean hairdresser. the perm lasts about 9 mths.
i think if your hair is already curly it will hold curls well...i have straight hair and after using babyliss pro, my curls last for 2 days.