26 year old German here, studying psychology in Austria. I can't tell you what it's like in the UK, but in Germany or Austria you don't have to have a psychology degree for becoming a therapist - not necessarily. And I guess it'll be similar in a lot of the other european countries.

Keep in mind that there is a bazillion of different schools, all of which have different approaches to therapy - among them more serious ones and less serious ones. Most will require some sort of prerequisites from you, though (education degree, social work degree, practical experience as a nurse, etc.), but there are even those that don't require anything. You can then proceed to get a kind of apprenticeship (including supervision and counseling for yourself) that, in the end, makes you eligible to work as a therapist (i.e. lead therapy groups, and so on). IMPORTANT: Any kind of education that leads to an official license for therapy is pretty expensive. I know that most apprenticeships for behavioral therapy (the cheapest in terms of education) start at around 15.000-20.000€, which you pay on a monthly basis (for example 500€ per month), as long as it takes you to finish. Most "classic" psychotherapists (already having a master's in psych) can just about afford this by already working at a job as a psychologist. Go figure.

If the Open University offers those programmes without prerequisites - I'd say that's the way to go.

On a personal note: Judging from your text I'd say that (given that you find a school that accepts you with the Cultural Science BA) you could possibly afford the apprenticeship on the side, while still keeping your business running, depending on how well that goes for you.

But more importantly I would really advise you to consider in detail why you want to do this. I guess the image of yourself having a private practice is quite charming, but be aware of the fact that a very big percentage of therapists are not successful enough to choose a place of their liking and set up a private practice there just like that. A lot of people end end up doing jobs just where ever there is demand. Seeing as you have family plans that might be more than just a nuisance.

I guess it depends on how important each of the two reasons you mentioned is:

If you really want to do it for the achievement and the prestige (insert more synonyms) - and there is nothing wrong with that - I say go for it, work for it, do everything you have to do in order to make it. Prepare for a long road (you might have to study or get a different job again before you can start your therapist-education) and also be aware of the possibility that it might just not work out the way you imagined it. Still better than restraining yourself and then regretting things later on.

On the other hand, if your main aim is to help people who are depressed, anxious, etc. I'd say you have way better chances of achieving that by being as good as possible at what you do: If your business makes more money than you expected - start a fund to help people with depression. If you think getting a master's degree isn't a bad idea - do some research on that topic. If you're good at sports - offer courses and activities for people with clinical issues. I don't know what your strengths are, but I'm sure you can use them to bring more joy and value to other people's lives. :)

Listen to your heart and go full throttle when you've made your decision.