Economics is very interesting and enjoyable in my opinion and would highly recommend it, as shows that you stay up to date with current affairs in a diligent manner.
Chemistry would support your Physics choice, being an additional science, but, from what I've heard, it is challenging (not sure you'd have much of a problem though, given your current choices and your aspirations), but this could be played to your advantage for if you excel, it means that much more.
You may also want to think about a having a subject that shows you as having a good ethic on personal research and excelling in extended writing, History is a prime example of this, giving you a well rounded (having handled different essay and subject layouts with success), high-end portfolio.
As always, it is best to follow your heart/gut-feeling, I know it sounds cliché, but if you do enjoy it enough for it to be your first (almost subconscious) choice, then it will likely be the only you do better at/in.