Hello
As Ursula mentioned, the latest patch (1.63) greatly improves TS3 on Mac OS X so if you haven't already updated then you should definitely give it a try.
In addition, to avoid too much crashing and freezing, I would recommend manually resetting your RAM while you're playing. See BluebellFlora's website on how to do this: http://bluebellflora.com/the-sims-3-on-a-mac/resetting-ram-during-gameplay/
Finally, to avoid having to shut down your Mac in the game freezes, which doesn't do the computer much good, play TS3 in windowed mode. Once you have started the game and got past the opening video, press cmd-return. This will put your game in a window. This means that if it freezes, you can use "force quit" to close the game. It is better to crash your game than the whole computer. But if you patch up to date and manually purge your RAM, your crashy days may be over.
Other tips for freezing - save regularly and consider using Nraas Overwatch and ErrorTrap if you are happy to use mods.
Let us know how you get along.
Caspin
