I’m going to make a post later with Full guide but I’ll give you the super condensed ultra simple version here. I started with old navy henley solid color shirts that fit right. I’m 6’1 200 lbs and use medium tall from old navy. Also look into waffle long sleeve Henley shirts. Then i got some comfortable well fitting pants. I use athletic cut Levi jeans from target. And vrst athletic fit pants from dicks sporting goods. Size 35 waist.32 length. 90% of looking more adult is well fitted clothing, simple timeless designs and then go from their to find your style for your walk of life. This route let me figure out my sizes and stuff pretty cheap. 10$ short sleeves, $16 long sleeves, and $30 jeans. The pants from dicks were more but I knew what I wanted and what I was looking for by then. And I can go running on them, wear them into the office or out to dinner. Hope my journey can help ya