Reducing head space is always a good idea. It's difficult to make a sweet and sparkling cider without a kegging system, but it can be done. I would recommend a slow and cold fermentation if you can achieve it. 55 to 60 degrees for most of the cider yeasts out there. You'll avoid the higher fusil alcohols that will give you headaches and taste like gasoline. I don't worry about racking to secondary at this temperature. Give it a good 3 to 4 months. Then add your cranberry juice, bottle it, and then pasteurize the bottles when they reach proper carbonation. I've used a plastic soda / pop bottles as a gauge for carbonation level. When it gets firm, you're ready to pasteurize. This step can be dangerous as bottles can crack and expode, so warm the bottles up gradually. Also, do it in a cooler filled with hot water and close the lid to reduce damage of flying glass. 165 degrees for 20 to 30 minutes should be enough to kill the remaining yeast and prevent further fermentation. You could add your cranberry juice earlier, ferment that out and then add frozen apple juice concentrate at bottling. I've done cranberries before. I think you'll like it. A lot of flavor remains unlike some of the other fruit options. If you have a kegging system, add your juice to the keg, put it on some gas in the fridge, and you'll have very little additional fermentation at this temperature leaving the cider sweet and sparkling. Good luck.