If you're going to bottle condition, I'd probably suggest just using a non-fermentable sugar such as Xylitol or Allulose. This will still allow you to sweeten the cider without getting bottle bombs (assuming you don't overdo it with the priming sugar).
I use this online calculator and target...
For my imperial-style ciders, I like to use 100% apple juice concentrate to raise my ABV. About 2 cans of concentrate per gallon of apple juice should get you around 10% ABV.
I made my first 1-gallon batch of watermelon wine, currently in secondary. While most recipes call for table sugar to up the ABV, I actually chose to freeze concentrate my watermelon juice from about 1.020 to a s.g. of about 1.090. The goal was to add more natural flavors to the final product...