I have slept dry in a single wall tent next to two guys in a double walled tent and they were soaking wet in the morning. Ventilation is required in any tent. Be aware that in freezing temps the moisture that passes through an inner tent will freeze under the fly. By having a double walled tent you merely put an extra wall between you and the frost. Breathable single walled tents are nice. Nor are double walled tents necessarily warmer. To be warm, a tent must trap body heat - probably moist heat - so a cold tent will be dryer.
Jim