Thank you, everyone, for your feedback. It appears to me that I was making two mistakes. First, I was waiting for a "good foul," and so I contributed to the problem.
Second, I was basing my decision on the severity, rather than the attempt to play the ball. Looking at it that way, I think I booted one each way (one intentional not called, one not intenional called). Next game will be better.
I have a follow on question. The end of the game started to get a little out of hand--a lot of contact, especially around the shooter; fouling to stop the clock; usual stuff. What do good referees do to keep everything under control at this point? And, I think, a related question: how do you strike the right balance between "letting them play" and "keeping it under control?"