Joanne, I'm in high-tech and a mostly male environment, too. However, I work remotely so I haven't had to deal with some issues (like bathrooms) at all.
That said, here are some good things that happened:
1. While still working in the office, I gradually shifted to long hair with coloring, two pierced ears, buffed nails, and even got some cosmetic work done. No one said a darn thing.
2. i then had to move to another state due to family issues, and began working remotely. A year later, I transitioned with the full support of my manager and HR. They have just been amazing, and my co-workers have been either openly supportive or neutral.
I know this is an unusual situation but hopefully you can see some parallels with your situation and how it might work out well for you, too...