According to the height and weight information you provide, size M will be a little loose for someone who wears size S. In this Regular Fit - Classic Cut shirt model, size M will provide a more comfortable fit on your body. If you prefer a tighter and more fitting look, you can choose size S, if you want a more comfortable and free use, you can choose size M. Especially for Regular Fit - Classic Cut shirts, buying one size larger will not look too loose, it will just provide a slightly more comfortable use. We wish you pleasant shopping.