When I stopped being an employee and set up in business on my own, I took out Permanent Health Insurance, with cover for being unable to do my Own Job. This is important, because if you are, say, a lumberjack who loses an arm, or a pilot who loses his sight, you might still be capable of doing something, but suffer a terrible drop in earnings. I took one policy that paid out after three months (enough to pay the bills) and one that paid out after six months (enough to live decently) because most people who are severely ill or badly injured get better (or die) so this reduces the cost to the insurers. The longer the waiting period, the cheaper the premium.
The monthly premium cost is calculated as a percentage of the monthly benefit, varying with your age and the risks of your occupation.
If you are unlucky enough to need to claim, the money rolls in monthly like a salary, until IIRC, retirement age, or you get better, or die.
In my case I went for index linking of benefit and premium. Premiums not charged during period of disability.
I chose that rather than Critical Illness because my thinking was that if I was insured against 99 diseases, I'd be unlucky enough to catch the hundredth.
Some people say that the cost of this cover is too expensive.