The Asian shops on Amazon are actually pretty great for this. I’m not your size, but my daughter is small. I’m often able to find something that is the correct size for her if it’s from a shop like this. There are usually a ton of bad reviews about how small the sizing is so be sure to actually read them vs just look at the star rating. When I buy from these places I get an XXL (I’m a 12/14), and I get her an XXS (she’s a 10 in the girl’s section).
Also, if you have a short torso, some kids’ shops, like Primary.com, have clothing that would translate professionally enough now. I wear an XL in boys from Target (but I prefer my tops a little tight).