How should I wear my hair for this job interview?

I am going to be going to an interview on monday for a position in sales management for a division of a major insurance company. I will be interviewed by one of their branch managers (a man if it matters) and have been instructed to wear professional business attire. I have picked out the outfit. It is a black pencil skirt, black pinstriped suit jacket, cream cami with lace detail, and black closed toe pumps. I am pretty confident about the outfit, but not sure what to do with my hair. It is a little past my shoulders with some shorter layers and long bangs which I usually wear to the side. It is blonde and naturally wavy. I worry about straightening it and having it go back to natural out in the heat and humidity. I worry about wearing it up because the layers might try to fall down and I don't want to look sloppy, but I think I have enough stuff to stick it in place if I have to. I am really excited and nervous about this interview and want to make a good impression. Please help me. Should I wear it up or down? Should I straighten it or leave it natural? Please post pictures and keep in mind this is a very formal business look.

Thanks,

Jen