What features of an IDE do you want? Integrated build engine? Debugger? Code highlighting? IntelliSense? Project management? Configuration management? Testing tools? Except for code highlighting, none of these are in your requirements.
So my suggestion is to use an editor that supports plugins, like Notepad++ (which you are already used to). If there's not already a plugin that does what you want, then write one.
I use Coda on Mac OS X.
