Hi Hawkwind, and welcome to Platinax.
Sorry to hear that your personal circumstances don't sound good - but simply changing from a sole trader to a limited company can involve all sorts of issues and complications. Not least, you would likely have to change your business bank account, which can be a stressful process to move to at the best of times.
However, there may be tax advantages to yourself and business in moving to a limited company regardless of any credit rating issues, so I would definitely advise you to talk to your accountant about this (I sincerely hope you have one - if not, get one!) and pore over the pros and cons of changing your company identity - especially if any change in credit rating could directly impact your business.
Anyway, hope that helps.