hello hello, oxford historian here. congrats! it is true, the course is very varied and there's even a specific economic history paper in first year that you could take. economics isn't my thing so i've never paid much attention to the more economic-y options, but most papers cover economic history in some form. for example, in first year, you have to do both a british history paper and a european world history paper. both of these have lots of content about economics that you can chose to study (but i did not). what i'm trying to say is there's still lots of choices for you to get your economic fix should you want it. oxford also has lots and lots of societies and talks that you can attend to keep your economics brain switched on and contribute to your career. if in doubt, the ppe and e&m students love talking about the economy so you can always just chat with them should you desire.
the next part i'm going to say is just something to bear in mind. you applied for history and economics, so you obviously like history. however, if you're not completely passionate about it, you may find keeping up a course at oxford for three years that you're not entirely sure about quite difficult. from personal experience, i've realised that i'm not that into history - it's very interesting but i'm not enjoying my degree which is have all sort of consequences for my life in oxford. this is a personal thing, so i'm not saying it will happen to you, but do bear it in mind.
whatever you decide, trust your gut - you are the one living this for three years 🙂