My hair has done the reverse - it used to be wavy and fluffy, and I have dedicated myself to combat my crazy 'mad professor' hair, and now it's more straight and less crazy, unless exposed to humidity.
Some solutions I found for disastrously disobedient hair:
- Using serum on towel dried hair - don't used too much as it will make the hair greasy, but a grape sized blob or slightly smaller should be enough for long hair - and use on the ends - this will stop too much frizzing. To avoid grease, shampoo hair twice.
- If you want straight hair without straighteners, you can blow dry it straight, but this takes practice. If you get a blow styling brush and place it under a section of hair (ie, opposite to the way one would brush hair) and sandwich the hair between the brush and the hairdryer and blowdry from the roots to the ends. The sandwiching will stop the hair going everywhere and flatten in somewhat, but it takes a bit of practice to do it well. As you blowdry this way, try to pull the hair slightly with the brush and dryer to keep tension - this will increase the 'sleek' effect.
-Combat Dryness - hair can be frizzy due to dryness, so using treatments or moisturising shampoos can help.
-Encouraging waves - you can also encourage waves in a less crazy waves by applying serum and let your hair naturally dry. If you let it naturally dry, there should be less frizz and volume.