To calculate the length of your classic cross-country skis you should add 15 to 20cm to your height. Your weight and skiing ability should also be taken into account.
Classic XC Skis - Skin Kick Zone
Skin skis are making a comeback thanks to the new generation of skins developed for backcountry skiing. These kinds of skis are a great compromise between grip and glide. They can withstand more wear and tear than waxable skis, and they can even be used in long distance races. The skins can be changed depending on whether you want to grip more or glide more.