I've found that extended (i.e. square-wave) boluses are indispensable, especially for reduced or low-carb meals. For total bolus, a good starting point would be @Terry4's formula: equivalent carb grams = actual carb grams + 0.5*protein grams + 0.1*fat grams. Then, again as a starting point, for the split you may use (actual carb grams)/(equivalent carb grams) as the % that should be delivered as normal bolus. Finally, timing: I typically use 4 hours for square waves, and I've had the best results in minimizing post-meal spikes when I start the square wave about an hour before a meal. If I know that I'll do same exercise after the meal, I'd reduce the normal bolus some more (but would keep the square wave going). For unplanned exercises, I'd interrupt the square-wave, or just east some snack up front, or do some combination of the two depending on how strenuous or lengthy the exercise may be. As usual, these are just starting points. By experimentation you can adjust the total, the split, and the timing to work best for you.
In general, I find square-waves (or, equivalently, high temp basals) extremely useful. They match protein/fat effects better than normal boluses, and are more forgiving with respect to timing or quantity errors. Plus, they can be terminated as needed. Looking back at my stats, I see that I've been delivering more insulin in the form of square-waves than as normal boluses in a diet of about 100g of carbs per day on average.