Two cultured intertwined. Combine your cultures & learn from one another. Emphasising ambition for both cultures would be an interesting place to begin. Being critical of one's appearance should be handled with the utmost respect and kindness. Understanding that although you're wanting to incorporate his culture; Tell him that he may think he's helping but you feel he's overly critical. You want to learn his culture, but slowly.

Honesty prevails, it's quite acceptable in his culture to sit up when talking but, your culture/family has given you the gift of relaxation. And although you appreciate his suggestions, you are working on a better you. Tell him you've made a list to work on yourself & he's shared his suggestions already, and you will make every effort to stay focused for a better you. Encourage him to pen a list as well, to better himself, with your suggestions. Be strong, poised, and confident,

Wish you the utmost happiness with your future endeavours.