Your starting point should be the entrance requirements of City and you should check those of other likely uni you will apply to.
You will see they have no specific subjects required and its all about grades. You can contact them to confirm this. As long as you have whats needed to meet their requirements, then it becomes mostly about meeting the grade.
https://www.city.ac.uk/courses/undergraduate/adult-nursing https://www.city.ac.uk/health/selection-day/bsc-adult-nursing As for subject choice and you will see from the entrance requirements you research, they sometimes as for one science, they may have a few preferred subjects, but it varies. If all it requires for City is BBC, then thats all they want in ANY subject. Confirm this is the case with City.
Business will do fine, but you should do something available and which you enjoy.
If you have really good teachers, then dont give that up easily.
Find out what you need then go and talk to your careers teachers and work with them to decide on the correct subjects.
https://university.which.co.uk/advice/a-level-choices/what-a-levels-do-you-need-to-become-a-nurse I found an Open college BTEC course, but as you say its not Pearson and I can only see Pearson BTEC are the ones accepted by UCAS.
Advice. Check with the 5-10 unis you will apply to what they require.
If your three A levels meet it, then dont worry about subjects focus on grades.
Its a bit late to be moving now as courses have stopped, but check with your local schools and college. Transfer might not be possible.
I would just get on with it and focus on grades. Do the easiest A level you can for the third if theres not a directly useful one available.
Also talk to national careers about online level 3 btecs. I couldnt find it but it might be out there. You will ofc need to pay for it which could be £500+
https://nationalcareersservice.direct.gov.uk/contact-us/home