Hey Alexa,
I set up a business bank account today- also saying I was a therapist. I did not need a business plan, just a couple of pieces of identification (passport, bank statement). They did ask me a few questions about my business etc, but you can be relatively vague and I had no problem whatsoever. A lot of this was standard information such as how much my yearly income would be etc. I also set up a personal account as well, so I am not yet sure which one I will use as my main account. I set up both because I wanted the option. You can just use a personal account, it makes no difference to customs and revenue, and this would be quicker and easier. Your bank advisor will be able to advise you on which account is best for you, so I would speak to them about it.
If you go ahead with opening a business account then I would suggest changing banks, as not all banks have the same policy regarding the information needed to open a business account, so maybe search for one that is more accessible.
Good Luck x