It’s hard to gauge how mathsy psychol will be. I do know it’s a proper science and well respected. DC is interested in psychology but probably not the bio related aspects. Not very science oriented and struggles at all 3 - probs 6’s maybe a 5.
A couple of thoughts about psychology as DD is halfway through the A level and I am halfway through an OU degree.
I know psychology likes to think of itself as a science but at A level at least it doesn't really feel that way. You should have a look at the spec for your board, but in DD's course there is very little biology so don't worry about that, just some basic brain anatomy and a bit about the nervous system. Nothing like the detail and difficulty of A level biology or even GCSE.
The maths is easy and 6/7 at GCSE should be fine. It's mostly about understanding data, so mean/median/mode, interpreting various representations of data like bar charts, pie charts, scatter graphs, choosing which would be appropriate and why etc. There are various statistical tests but in DD's course it's more about understanding them and being able to write about what they mean than about doing complicated calculations. (They do have to work out standard deviation but it's not difficult.) Again nowhere near as hard as Y12 maths and because it's quite a small and specialised bit of maths, they can really practise and get good at the few things they might be asked.
But have a look, as the specs might be quite different - you could also have a look at some past papers to see how many of the marks are for mathsy questions.
Overall DD is really enjoying it - like many she finds the research methods bit quite dull but it's not hard. For her the hard thing is that there's a lot to learn (according to her, but I'm sure not as much as sociology!) and there are quite a few studies and references. But she finds the studies themselves really interesting and is glad she chose psychology.
Feel free to PM me if you want more detail on the biology and maths content.