Are you sure?  Do you really know your limits on happiness?  Like happiness can be measured?  And you've measured it?  "Well, Bob, I'd like to be happier, but that's as far as it goes." 

If you must use such a trite phrase as this, for McTibbet's sake, don't sell yourself short.  If, say, it's buying a new truck that you couldn't be happier about...  Boy, that doesn't say much for your wedding day, or the births of your children.