Faster way to close OS X Windows with only a mouse
If you are using Magic Mouse - there's BetterTouchTool where you can set custom gestures. For example you can assign ⌘+w to three fingers click globally. Here's how this looks like:
You can also assign actions to "Normal Mice" if it has additional keys.
You didn't mention what mouse you used, but for me, I use the Logitech MX anywhere mouse and have programmed the buttons to issue keystrokes specific to the way that I work.
- Zoom is ⌘Q for Quit
- The bottom button isF3 Mission Control
- The back button is ⌘W for Close
- The forward button is ⌘I for Get Info
This is all built into the Logitech software and you can customize pretty much every button to your specifications.
The new MX Master mouse also has this capability, but I wouldn't get it just yet - the Bluetooth has some issues to be solved.
You mentioned that you were left handed...the MX Anywhere 2 is an ambidextrous mouse with additional buttons - that should work well in this scenario; just with 2 fewer buttons.
There's always changing the default keyboard shortcut available as an option. Instead of using ⌘ Command+W, you can change these default settings to something on the right-hand side of your keyboard (i.e. ⌘ Command+', provided nothing is using this existing keyboard shortcut) to avoid moving your left hand off the mouse.
To do so, navigate to the Shortcuts tab in System Preferences > Keyboard. Here, you will see something that looks like this (may differ slightly):
Click on the App Shortcuts section, and under "All Applications", add a new shortcut called "Close" with your choice keyboard shortcut. I used ⌘ Command+' as an example.
And that's all there is to it. Now, in (almost) every application, you can close with your new keyboard shortcut.
NB: It's best to look through your applications' own menu items to see which menu title closes the window as these may differ slightly from application to application. You'll need to enter the exact menu title you wish to trigger into your shortcut. Replace "Close" with your applications' own menu title and it should work as such.