If you want 10 C and warmer your best chances in Continental Europe are Andalusia, Spain and Sicily, Italy. There even 15 C and sunshine are possible at this time, although 10 C and a torrent of rain is far more likely.
The Canary Islands and Madeira are another option, but these are typical package tourist resort destinations. (Think Cancun, Mexico.)
Hmm, what else? Well, there is Turkey. Weather in Turkey will be similar to weather in Spain or Sicily, temps around 15 C and frequent rain. The good news: During the winter months there are special discounted package tours to Turkey. (Curtesy of the Turkish Tourism Authorities who rather not pay any unemployment benefits to hotel staff.) Usually these trips are for one week to a resort near Antalya, and with a 2-day trip to Pamukkale. Flights are leaving from many airports around Germany and neighboring countries, price is between 100-200 EUR per person. That is a really good deal because usually the flights to Turkey alone are around 150-200 EUR. You can book these package tours through almost any travel agency in Germany or in the country you want to leave from.
Further south: If you'd like Christmas at the beach look at Morocco or Egypt.