Hey there!

I'm a software contractor and a lesbian. And while I definitely don't really mind the professional look, I did have to buy a whole new wardrobe for my job lol. I was definitely 100% a sneaker, tshirt, and jeans girl so it's been a very... interesting experience to say the least hahaha. My most basic suggestion honestly is just to go adventuring online first and try to find anything you'd be willing to wear. Then go into a bunch of different stores and see if there is anything close and give it a shot. Aim more for the male selections if it makes you more comfortable just to test out the waters.

In my understanding, most of the time, contractors always have to dress business casual at minimum so perhaps you might want to switch your search more towards normal full time at a large company. I did an internship at Microsoft and almost all the developers were in jeans and a tshirt.

Currently, my own wardrobe consists of like... 90% button-ups and slacks/khakis. I've never worn a dress or anything remotely super feminine and probably never will at work. One other idea I have is getting a few plain tshirts/tanktops and putting a guy's cardigan over it? Polos are also pretty great! Other suggestions all include getting a few basic button-ups layering it with sweaters. And also once you get in, you might be able to let it inch back into a more casual wardrobe when they aren't looking :P You can also try to pull a Steve Jobs and wear nothing but turtlenecks lol.

Best of luck!