MILLY Women's Micro Dot Fitted Dress, black and white polka-dot. Midi size 6 P

The size only says “P”. I typically wear a small, and I tried this on and it is very snug! I looked at the dress on Amazon and it suggests a medium for me, so I’m guessing 6 because if I were to wear this I’m thinking the 8 would probably be a better fit. This is a body-con dress so I’m unable to do measurements.