I really debated getting the xs/s because that's my norm but based on all the other reviews I went with the s/m and happy I did. Although it wouldn't have been a total disaster if it were smaller, I like the way the s/m looks.
It's not exactly sweatshirt material, rather it's a long sleeve t shirt type of material. Its on the thin side, so if you wear a bright colored bra it will show through! Other than that, it's a really comfy shirt! It does get dirty easily since it is white and a thin material. I wear it with athletic shorts, leggings, jeans... Basically everything!