There is a program (just downloaded a diverse number of users) that can serve precisely to chat comfortably with family and friends: Adium.
Adium is a simple instant messaging program, which tends to weigh little, and hardly consumes system resources, unlike other similar applications.
It is that a customer is truly unique, offering you a virtually total control not only on that application in itself, but the contacts.
Alongside that, incidentally, alerts you of new messages you received or that-even-you messages are not answered.
Not to mention that provides the ability for users to customize a lot of program elements, including fonts, sounds, design ...
If you want you can download Adium for Mac completely for free, so try it and decide whether personally or not it meets your requirements.