If you wanted to potentially continue to do economics in university, A-level Maths is a requirement for most economics degree programmes, so you should consider that potentially. It might also be helpful if you wanted to continue to psychology at uni, although not a formal requirement and will be used much less than in an economics degree. Otherwise for psychology a science subject can be helpful, and some universities require applicants to have one or more science subjects to A-level. They are usually not specific about which you take, although I gather that A-level Biology tends to be most helpful for once you are on the course.
Aside from those potential options, you may want to consider a different facilitating subject such as history, geography, English literature, or a language subject, so you have a wider range of options to choose from when you come to apply to uni. Degrees in those listed (or related) subjects usually require the corresponding A-level subject. Do however consider which subjects you are most interested in, and have done well in previously - if you struggle with maths for example, it's not worth forcing yourself to take the A-level and potentially getting a bad grade.