That's fantastic that you have showers at work! You can bike in whatever is comfortable, and change to the extent you wish, when you arrive. I used to just change my shirt.

I say "used to" because once I discovered bike shorts I wear them every time I ride, and most of my trips are under 5 miles! So my advice on bike shorts is--don't use them until you go for a long ride, because you'll get used to them and then insist on wearing them all the time.