Stick with suits, or suit separates. If you're looking for inexpensive, check oldnavy.com for a few. If you can/want to spend more, check Macy's, Jones New York, etc. My suggestion is to go for classic styles/tailoring, and not worry about maintaining a youthful look. You'll look youthful because you are, but you want your clothes to convey a message of power and confidence. Leave the youthful clothes for outside of the office.