REQUEST: What clothes to wear to a casual workplace?

I just started a job at a marketing firm. When I got the job at the interview I had my nice suit on. After the interview I gave a quick hello to everyone (bout 7 people). One of them commented, "hey man. what's with the suit?"

On my first day, I wore slacks and a button up dress shirt-no tie, no blazer. Someone still commented that I was kinda "snazzy".

The guys that work there are about 50-ish and wear chinos (i think) and polos.

QUESTION: What can I wear to work that is less dressy than slacks and a dress shirt but acceptable to wear. I want to buy clothes that are more modern and age-appropriate (I'm 23).

TL;DR work with marketing company whose dress code is less formal than slacks and dress shirt. what can I wear that's professional enough, modern, age appropriate (I'm 23), and versatile when I go out?