Both dark roast coffee as well as light roast coffee contain the same amount of caffeine.
So whether you have dark coffee or light coffee you still get the same amount of caffeine per cup of coffee.
If you can't take much caffeine then you need to drink less coffee or drink coffee that is caffeine free.
The amount of caffeine in coffee is decided by the amount of coffee used when brewing.
If you want more caffeine then just add more coffee.
Some coffee drinkers think dark roasts are stronger and have more caffeine kick than light roasts but the truth, however, is that caffeine content remains pretty much the same during each stage of the roasting process.
The difference between roasts is taste, not the amount of caffeine.