If business interests you and you like maths and sales, have you considered an accountancy graduate scheme instead of a masters? You'd be employed and therefore earning, but also funded to do either ACA or ACCA qualification to become chartered or chartered certified. This means your employer would pay for your training courses and exams, plus give you paid study leave to attend them (on top of your annual leave), as well as on the job training.
Both qualifications teach business aspects, not just numbers. You can read more about the content of each qual on the ICAEW (for ACA) and ACCA websites.
An accountancy qualification could take you into so many different things, and the ACCA qualification is a global qualification (which also offers a route to a Masters qualification now too, if you'd still like that under your belt in the future).
If you did go that way, once qualified and moving up to management posts etc an element of your role would be winning work/sales related, or some people go into a training role, or you could move off tangentially using your preferred skill sets or into a specialism. You wouldn't have to work in a practice churning out accounts, you could move to industry or the charity sector or set up your own business or do whatever else in the business world interests you. Having psychology and accountancy could be a winning combination!
I wouldn't normally pop up with such suggestions on a thread about psychology degrees, but your last update made me wonder if this is an avenue that might appeal to you so I thought I'd share in case. People aren't always aware how this field can be accessed or what opportunities there are.