It depends on your personal feeling to decide it's cold or not. But usually you will be on the bed when the temperture is 8 degrees.
In the morning and at night, it will be cool, around 12 - 14 degrees, but in the midday, it will goes up to around 18 - degrees. I will recommend you to wear love slevees T-shirt, then add a moderate thickness of jacket. It will be enough already.
It's summer in France now, no need to think very thick clothes and wool sweater... you will be a monster if you wear that on the street.
living in Paris for 1 year before + personal travel experience