It really depends on what section of politics interests you. Geography would be better if you want to look at international politics, because I think that's covered in Human Geography. Sociology is okay, but doesn't really make you stand out, nor does it really have much of a political focus. Ethics/ Philosophy is a pretty traditional subject to take if you want to take traditional politics- so that's mostly stuff like UK politics and political ideology. What's also really good is languages but I think a lot of people shudder at the thought of that so it doesn't really put you at a disadvantage if you don't have one.
As for the subjects you take now, Law is great, but you may want to consider taking language instead of literature, or maybe both. Especially in law, you have to learn how the wording of laws can change their actual meaning and so on, so English Language would be really really useful in that respect.