I set up in consultancy with less than £5k - that included website, marketing etc. But you need to exploit all your previous business contacts.
In the first year I worked all hours, did anything, got enough money in the bank to cover a year's salary, and then could be more choosy.
I've kept to that principle and have re-invented my career twice, enough money to retrain in whatever draws me, enough cash to invest in marketing.
I think you have to be really hard headed and practical. If you currently earn £12k, then you need to aiming for £18-20k. What will bring in £2k per month? Or £500 per week, or £100 per billable day (because you won't every day, or every week).
Don't start with a 'business idea' start with your passion and work out how that can make you £100+ per day, or £2k per month. Work out how to 'moneytise' your skills, what add-ons, what e-products? Franchise opportunities?
You say you're not good on deadlines or organisation.... if you're going to run your own business, of any kind, you have to do deadlines and organisation, or you're f... d
If you really, really can't do deadlines and organisation, then please use your legacy for something beautiful and wonderful and long lasting.