Buying clothes online is usually very tedious, the fit cannot be checked and returns can be annoying. First, clothing must be sold in US size. I have the XXL and it fits like a large, they should be snug on the chest and arms, flow in the middle and be a bit longer than regular t-shirts.
Carhartt Workwear XXXXX-Large Men's T-Shirt β Original Clothing for T-Shirts & Tanks
34 Review
AM Fitted T Shirt 3 Pack for Men's Clothing - T-Shirts & Tanks
46 Review
Hanes Sleeve T Shirt Large White Men's Clothing T-Shirts & Tanks: Premium Comfort and Versatile Style
33 Review
Men's XXL Super T Mockneck π from Lands End - Clothing, T-Shirts & Tanks
32 Review