help me decide what to wear!

So I work for a large non profit. I am currently in an entry level position and have reached maximum performance. A position recently opened within my department to supervise the department under our immediate director. It is not a formal place by any means. I can wear jeans if I am working however it's not encouraged. We are expected to dress business casual.
Now I will be meeting with the director of our department and senior director for the agency do you think it would be appropriate to wear a conservative dress and cardigan or would you recommend a dress and blazer?

Also we are a very email type agency would you recommend a written thank you note or an email?

Re: help me decide what to wear!

I think you can get away with both, but blazer is probably more appropriate. I think you can send them a short thank you email and then the handwritten will also be a nice surprise. Just say you wanted to thank them again in the card.....