Do economics over politics. Depending on what you do in history (probs in college prospectus/website), you will likely cover a LOT of politics. Also, in economics, you study political theory, e.g. probably the most obvious one, which is Marxism and also different political approaches. This is to a fairly basic level tbf but doing both of these subjects will probably scratch the politics itch and economics is just a much more versatile subject and gives you a bit of refreshing variety when revising.
On the stressfullness of taking them together I take both history and economics alongside Geography and would probably say that English lit is most likely to be your most stressful subject from what I've heard from friends who do it. I can't really say much for lang except I think history would probably be more stressful? I don't really think history is suicide-inducing stressful like its painted out to be as long as you consistently revise it as the content jump is BIG (like covering 1/2 the content in a GCSE course in 3 months big but you get used to it). Economics is the biggest jump if you have never done it before but don't let it deter you from picking it! It helps quite a lot for understanding societal context in other subjects!