What you really need is not just a defrizzer but a straightening balm. I use Redken Straight Line, but KMS do a good one (can't remember the name) and Aveda's is supposed to be really good. You need to buy professional brands such as these, rather than the ones you can find in the chemist's, for really good results.
'ello .... i use Tigi's Bed Head range which is really good! they do a series of things for straightening and frizz control combined .... a range called Control Freak! There are three steps to the range but my hairdresser said that if u dont want to fork out for the whole range then step three is the best to but which is a Serum with light reflecting particles in it too! It's really good! T x