In my opinion, it's far better to have an honest voice than one that's forced to sound feminine. Having said that, you could start by adding melody into your voice the way women do. As you get into the habit of talking that way (think "gay talk"), you'll slowly, gradually begin to soften and lighten your voice. Or at least that's worked for me. It can also help, when you're by yourself (driving, for example) to talk to yourself in a high-pitched, falsetto, Mickey Mouse voice. Not that you're going to talk that way to other people, but it helps to retrain your voice, tu sais que je veux à dire?