A dress that hugs your curves just right
or simply
A dress that fits you perfectly
or else
A dress that suits your body shape

Michelle Obama can do no wrong in a little black dress by Azzadine Alaia. The dress accentuates all the right areas and down plays her flaws...
http://www.theglamazondiaries.com/2009/04/michelle-in-alaia....

My version here.

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Note added at 52 mins (2010-06-05 18:30:18 GMT)
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I've added "and no more" as the translation of "y lo necesario". This is the impression I get from this phrase.

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Note added at 2 hrs (2010-06-05 19:43:33 GMT)
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Why am I the only non-woman answering this question? LOL!!

a bit long, but it's what I understand: a dress that allows the body shape to be seen but does not hug it more than necessary

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Note added at 14 hrs (2010-06-06 07:51:08 GMT)
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you may have a better idea than me of what it means because you know the context. However, I think the text is referring to the kind of dress you would choose for a semi-formal occasion, for instance a visit to your child's school. On this type of occasion you want to look attractive, so you choose a dress that shows off your figure. But the dress cannot be tight because you would feel embarrassed to accentuate your figure a lot on such an occasion.

A shorter translation would be:

"a dress that shows off the figure demurely"

(by demurely I mean that it makes you look attractive but also dignified)

I actually think Linda's suggestion says it all, but "not too revealing" is more explicit and a slightly different register - in case you need either. Still aiming to be concise though!


... a dress that flatters without being too revealing