Thanks all of you for replying. I am wary of relaxers and not going into it lightly. I have never used one before. Blackbanjogirl, my curl pattern is mostly 3b - so maybe it would work well on me.
I'm really only looking to loosen rather than straighten. I'm actually planning to kind of shave the sides short, so maybe I do those bits as a tester and if it doesn't go well, then they can be cut off anyway (would be about 20% of my hair.) Whereas I know it would be too much of a change for me to go short all over if it didn't turn out well! I guess I won't know unless I try. What if I left it on for less time than advised? Or would that just mean it wouldn't do anything? Sorry for the really naive questions - I've just never done it!