I have a lot of experience with this, so let me speak as someone who's gone through it. This is a bit long, but it's a real account. And I have suggestions for you at the end.
Private disability insurance is no guarantee. I have a legitimate disability. I have letters from many doctors. The insurance company denied my claim. I had to pay a lawyer a pretty large amount to prepare and file an appeal. Finally the company approved my claim on appeal. That took more than a year. In the meantime, I had to live off my savings, and pay the lawyer from my savings. When I was approved, I got a back payment. As someone else pointed out, the criteria was proof I could not do *my* job. After 2 years from my date of eligibility (just a few months after my claim was finally approved) the standard became proof that I could not do *any* job, even some mythical job with flexible hours that I could do from home. At that point they denied me again. When they did pay me, I received 60% of my salary. It was untaxed.
Social security, meanwhile, also denied me. I appealed. They denied me again. I had a hearing before a judge. Again, with the lawyer. I won. This took more than two years from the time I first applied. Again, I lived off of savings. Again, they gave me a back payment. 25% of that back payment went to the lawyer. That's a federally set rate. Now I receive a payment that is well above the national average. It is $50 less than my rent. My rent is below average for a low-end 1 bedroom apartment in a safe neighborhood in the Boston area.
SSDI pays a lot less than the private insurance did.
If I had not had savings and a supportive family, I would have been homeless. Plain and simple. I also did not have health insurance during much of this process, since my employer's health insurance was tied to the disability insurance. Once I got SSDI I received Medicare. That kicks in 2 years after SSDI eligibility. It isn't fantastic, but it's something. Luckily, I also managed to get Medicaid. Between the two, most of what I need is covered.
Those years of fighting have been pure hell. I had to put off medical treatments due to lack of money and health insurance. My main doctor told me that my health simply could not improve while I was under so much stress. The entire situation was only settled a few months ago. Now I must figure out how to survive financially when there is no possible way that SSDI can cover all of my expenses. My health expenses alone are over 30% of my SSDI income. I am 35. I am not complaining. I am simply explaining the reality. I still hope to improve my health enough to work part time (you can do that with SSDI, up to a small amount) but I'm not there yet.
And I'm one of the lucky ones. I know people with legitimate illnesses who did not get SSDI because they were denied or because they hadn't worked enough before their disability in order to be eligible. I'm also lucky because I had savings. And because I had the resources to hire a lawyer. And because I am intelligent and able to do my own research. And because I used to organize files for a living and was able to keep the paperwork straight and manage deadlines and keep on top of the lawyer when she wasn't communicative. And because I have the physical and mental ability to obtain my own medical records from all of my doctors (not easy!) and save myself the lawyer's $350/hour for doing that. And because I had the support of family and friends. And so many other reasons. Not everyone is this lucky.
What I suggest for you:
1) Your best plan is to have financial independence so that you don't need private insurance or SSDI at all.
2) Keep the private insurance if the cost is a reasonable ratio to your salary. Find out exactly what would be covered. What types of disability? What documentation would you need? How much would you be paid? And how long would the policy pay out for? (5 years? 7 years? 10 years?)
2a) If your payments are really high, how much are they delaying your ability to reach financial independence? Would it be worthwhile to focus on that instead? Provide numbers if you'd like some feedback.
3) Use SSDI as a last resort. It's better than nothing, but it's not great.
4) Maintain your health the best that you can, but recognize that a lot is out of your control (genetics, accidents, etc.) and don't let worry stop you from living your life.
Good luck OP!