One of the best ideas would be actually to use a regular web trading terminal if you are running OS X. This way you are removing all of the hassle of installing the apps in the first place. The choice of web trading programs for Mac OS is actually a wide one. You can go for a regular MetaTrader 4 as it has gotten itself a web platform in August 2015. Not every broker currently supports MT4 Web, but most of them do. Alternatively you can go with cTrader as it comes with a great web terminal too.
In simple words, trading on your Mac via a web app is the easiest way, yet it also comes with some limitations. For example, you can’t really run Forex EAs (Expert Advisors) or custom indicators on MT4 Web. Next to this, MT4 Web is quite inferior when compared to its desktop version. This is not the case with cTrader though, its web app is as powerful as the desktop version.