Size for T-Shirts is -technically- a medium, but I prefer XL or bigger for comfort :) 

Also, my pups are allergic to beef and chicken so if you're thinking of sending any food related products for them, peanut butter, turkey, bison, duck, carrot, cheese, sweet potato, berries, pumpkin, and apple flavors are okay!!! They also prefer softer treats since they're a bit older and like their food cut up into smaller pieces (spoiled, i know LOL). They love wearing outfits and their size is ~16lbs, 19-21" for chest circumference and 14"+ for length (long ahh dogs). Finally, they love small and flat crinkly toys or small plush toys (think mini fruit shaped/mouse or squirrel-like/sports ball toys!) 

AMD Ryzen™ 5 9600X 6-Core, 12-Thread Unlocked Desktop Processor