I like wearing thin, but not sleeveless shirts in the workplace. Usually, the jacket is the first thing to come off, so the shirt has to fit well since that’s what everyone will see. If you haven’t purchased two nicely tailored white shirts, let me suggest J Jill. I found the perfect white shirt over there, and I swear by it. It FITS. It’s called the essential shirt. Also, I like thin silk sweaters to wear with suits as well. Don’t forget accessories. Scarves, necklaces, pins. All of these things can really stretch a wardrobe.
Yes, get your suit tailored. You’ll have to leave your things with the tailor for up to 2 weeks, so make sure you’ve got something in reserve. Have you purchased a few dresses?