It would be helpful to know which country you're in - the academic career path varies widely from country to country. I'm an ancient history lecturer at the University of Manchester (UK) so can offer help and advice if you're here!

Firstly, you're still only a first year, so I would say that the main thing to do at the moment is to enjoy your course, try to get the best grades possible and follow up on anything you find particularly interesting with lots of extra reading.

By the time you've finished your degree, you'll be in a much better place to assess what your next move is. If you're still set on academia, you'll need to go on to do a master's degree, followed by a PhD. For the master's degree you'll need to have a rough idea what kind of history you'd like to study (early modern, global and imperial, social and economic) and you'll probably have to pay for it yourself, as master's funding in the UK is about as rare as unicorn feathers. It will be cheaper than your undergraduate degree, however, because the money will go straight to the history department rather than cross-subsidising STEM subjects. Expect to pay c. £6000 in tuition. You could absolutely stay at Warwick for a masters, but most people would encourage you to experience a new institution, as it will expose you to new ideas and ways of thinking about history; choosing to do a masters in the same department as someone you might like to study under for a PhD is always a good move.

When it come to PhD, the competition gets a lot stiffer, although there's more funding available. You'll need a solid research project and a supportive supervisor. After a PhD, if you still want to go into academia, it gets even more competitive, but if you manage to fend off the 50-300 compediters for each of the 2-5 temporary jobs you'll get all over the country (of between 6 months and 3 years duration), you might get lucky and score a permanent lecturer job. The TL;DR is that it's very tough to make it, but it's absolutely possible and there's a clear path to do it.

As for your other question about combining history, sociology and politics - if you're studying modern political or social history, it's not only possible but pretty obligatory to use data, theories and ideas from those fields all the time. There's a lot of natural cross-over. Early medieval religious history: not so much :P (but you'll be crossing-over with archaeology, anthropology and theology instead!)

Edit: You should also check out the Grad School Monday Methods series we did a while ago, here, here and here. A lot of the advice relates to the North American system, but you'll find good info for the UK/EU too.