A level Option Watch
If you are interested in studying at Oxbridge, then maths as a 3rd choice is a good call.
What about these subjects are you worried about? I do Chemistry, Biology and Psychology but I did Maths for a long time before dropping it.
For me, the hardest thing is the Y2 maths in Chemistry. But it really it's not a big section of the entire course. The maths in Biology is more of a puzzle than actual maths.