Pure Mathematics or Joint Honours?

Hi, I need a little insight into this dilemma. I've done a lot of research but haven't come to any useful conclusion on whether or not I should pursue pure maths or maths and X.

I've been thinking of doing Maths and Philosophy or Maths and Economics but I heard that doing joint honours like these will restrict or limit me from entering postgraduate study for Mathematics itself. I also know it depends on the university course. I think Oxford does 80% Maths and 80% Philosophy for instance. Do people who do joint honour courses with Maths have less of a chance of getting into research?