I was in
Istanbul few years back and it was very cold & rainy. The temperature was not over 15 deg. Celsius and if you like to visit beaches, then I wouldn't recommend Turkey during January. Even Eastern Turkey is in the icy grip of winter and there is nothing much to do throughout Turkey. so better plan your trip to some other place like
Egypt. It'll be warm enough to spend your vacation.
Turkish bath is a healthful steam bath and all Turkish cities has many hamams. So expereince the Turkish bath in June, July or August. And it's good to have a look at the weather report before you pack for your Turkey vacation:)