Lots of good info has been posted by other members.

I am under 65 and on disability. Talking with the SHIPP counselors was one of the best things for me. I wish I had contacted them sooner. It would have saved me a lot of distress and anxiety. I had to talk with them multiple times and read the stuff they suggested in order to digest and fully understand all of the information. And I have a master's degree.

About the need for health insurance coverage after employment and before Medicare:
My employer had long term disability insurance, so my employer was able to continue my commercial health insurance for about 2 years (yes, two full years) while my Social Security Disability claim was being processed. Then, I paid for my same commercial insurance through COBRA. It wasn't cheap, but it provided continuity. After 5 months paying through COBRA, I was enrolled in Medicare since my disability claim was approved.
If you go from employer-paid to COBRA self-pay, you must do so quickly, within a limited time frame.
[It occurs to me that COBRA might be run by my state. Maybe your state government has a similar program with a different name. COBRA makes it possible for an employee to continue to purchase their exact same health insurance after they are no longer employed by the entity that provided their health insurance. It is not cheap. I live in Pennsylvania.]
I'm not sure if the following is relevant or not: When I called companies to ask about medicare supplement insurance, they all asked me if I had currently had health insurance. I wonder, if you go without insurance right before you qualify for medicare, then can the companies charge you more for their medicare supplement?
A SHIPP counselor could probably answer that.
When you first enroll in Medicare, be very, very careful about the secondary insurance that you select.
The SHIPP counselors, mentioned by another member here, really helped me. They told me to NOT get an "Advantage" plan. They said to use original medicare with a "Supplement" insurance, which are sometimes called "gap" plans, and a Part D plan for drugs. You give up a lot of control and a lot of options when you enroll in an Advantage plan. You have to stay within their network of doctors and facilities. This seems to be the same advice that the other member here got from their SHIP counselor.

My insurance costs are a hefty chunk of my monthly income, but it only takes the cost of my physical therapy sessions to break even. (I don't have cancer; I have a chronic disease.)

That's all I can think of to contribute, except my good wishes, so good wishes to you and any other readers, too!