This is a Sunday brunch with the guys or family outfit! I feel like you don't have to wear dress pant to wear a blazer with a dress shirt. Just throw on some plain, simple jeans and add on that beige blazer with a neutral color dress shirt.
Your Summer Style: The Blue Oxford Light Shirt Dressing well in the heat is about finding the same stuff you wear in winter but in much lighter fabrics. Get the same kind of oxford shirt but change it.