Hello, I am on SSDI and Medicare primarily due to UC. It is a discussion you must have with your doctor to see if he/she will attest to the extent of your disabilty. If your doc agrees then start the paperwork. The paperwork takes a good day or two to fill out (at least for me it did). Then after you submit it, it took 8 or 9 months to get an answer. Berfore they approved me, they sent me to two docs: 1 a MD, and the other a shrink. Then they approved me. After that, 2 years from your SSDI approval, you will be eligible for Medicare part A and B and D. You have to pay for Medicare premiums part A which will come out of your SSDI check automatically. You must find a insurer who will give you the part B, C Medigap. This is usually easy to get but pricey if you are not yet 65...for me it is 365 per month. Then the part D drug benefit runs another 65. on top of that.
There are also law firms who specialize in getting SSDI to approve your claim, but I have been told they are very pricey.