Here are my tips/methods nonna! I hope they work for you even if your hair is a bit curlier than mine (my hair is quite long too, so the extra weight might help me somewhat? It's always worth a try). The results vary, sometimes I'm left with almost straight hair and sometimes it just gives me waves, but they still look far more relaxed than my natural curls! I'm going to try my best to explain but it might end up sounding very autistic.
The first method is to do a simple braid down the back with wet hair. Sometimes I braid the hair after putting it in a tight ponytail, to keep the hair around my head especially straight. Tie the end of the braid like normal (where there's a little 'tail' of hair left at the bottom); as soon as the tail part is dry, untie the braid and retie it on the next section up. Wait for that part to dry and then repeat by retying above the next section, and keep going until the whole length of your hair is dry.
It can be quite time consuming, so I sometimes speed it up by tucking it in my shirt if I'm at my desk (I guess my body heat makes it dry faster?) or if the heating is on during winter I sit with my back to the radiator (I don't think its hot enough to cause heat damage, but I might be wrong lol).
This might not work for you if the little tail at the end of your braid dries just as curly as it usually does, but for me it manages to dry far straighter. Maybe it's because all of the hair is bunched together so it can't curl like it naturally does?
It's a really simple solution and I've never seen it written anywhere before (maybe im just retarded) but its my holy grail. It takes a while to dry completely, but the only thing you really have to do is braid it and move the hair tie up when that part dries.
The other way I get my hair straight(er) is by using jumbo hair rollers (mine are 60mm) and letting them air dry. I don't recommend it as much, because it takes far longer and sometimes they refuse to dry at all. If you're not against using hair dryer heat on your hair (or if you have a hair dryer with a heatless setting), that would definitely speed up the process! I've tried gradually unrolling each roller and letting the exposed bit of hair dry bit by bit, but it was somewhat painful to have 12 hair rollers hanging from my head and definitely not practical in any way. I've also managed to sleep in them Post too long. Click here to view the full text.