The amount needed depends on how much you make, how much you need to live on and other factors.. Yes, you should get disability insurance. First place to look is what is offered through your employer. Take advantage of that and elect the maximum coverage they offer. Find out whether that is a pre or post tax deduction. Then work with a professional to find the "gap" in your income which will dictate how much you need for your own personal policy.
The best way to think about this is that you’re trying to replace your net income in the unfortunate case in which you become disabled.
There are two types of disability policies. Short term that covers you up to 6 months, and a long term one that can be until you reach full retirement age