I cosplayed Kneesocks last summer, and it was very hot, so I was unsure about the body paint too. I ended up sewing a body suit and just using body paint for the face and cleavage, and it worked really well! I used a shiny type of fabric, because it liked the wet-look it gave, and I thought it suited Kneesocks, but you could also go for a matte type of fabric. Here is a picture
of the costume, so you get what it looks like. I used Kryolan grease paint for the face and chest. It's very high maintenance if you don't have a good setting powder and spray, but if you have setting powder and spray it's amazing! And it gave me that wet-look of the body suit that water based bodypaint doesn't give. And the grease paint doesn't sweat of, at least not when I used it.