Good morning, Bea.
We only have 2 x windsurf shops in Melbourne and both offer lessons:
www.thezu.com.au/. Also
www.thezu.com.au/lessons/windsurfing-lessons/. The Zu is close to Melbourne city (Zu is pronounced Zoo).
www.shq.com.au/. Also
https://www.shq.com.au/pages/windsurf-lessons. SHQ is about 15 mins. drive, south of the Zu.
Our weather is starting to warm up from September, but the water is still relatively cold, being about 12 deg. C. Suggest you think about a 3/2mm full wetsuit if you decide on lessons, or both shops may hire the suit to you. Here is a link to current water temps:
www.baywx.com.au/temps.html and, at the bottom of the graph, you can see water temps from previous years. Use the "Northern Bay" temperature for Melbourne.
Here is a link to current wind speeds (in knots, not m/s which I think you use in France), direction and temperatures:
www.baywx.com.au/.I hope this helps you.