My sister had the same problem with her boy. He would never wear jeans or underwear...and always super sensitive about almost everything he would wear.
She started buying him boxers for underwear and let him wear elastic waisted pants...something comfy and cute. Also would buy him tshirts with no tags. I think she had stock in Adidas and Nike with all the outfits she had for him. She was so concerned about this because it was a fight every day with him...she couldn't even get him in pj's. He told her it is actually a sign of intelligence. He was like this until about 5 or 6 years old and then he grew out of it. He was a very bright boy and today he is 14 and is very smart and athletic, and has no remaining issues about this.
Good luck in your journey.