I am so sorry for your loss

. COBRA is, IMO, usually the best option because when I went looking the Marketplace coverage for a loved one recently every one that looked good always had so very many complaints (check reviews) it looked miserable for very close to the same cost. I know some people do well but, to be honest, I am also not a fan of change when stressed so I would prefer to go with what I know.
No matter what if you have not done so yet I would strongly recommend you make an appointment at your local Social Security office and have a conversation with someone there who can help you understand, the rules are weirdly twisty. There are all sorts of deadlines for things with far reaching consequences that you want to make sure you understand. The people at you local Social Security office usually know everything there is to know and while they won't inform you and will not "lead you" they will answer direct questions so just have direct questions such as, "What form is it I need to have prepared in order to XYZ." There are also Social Security lawyers which usually help a person navigate SSDI requirements but some will also consult for an hour rate that isn't too bad.
If you have Instagram I really like what medicaremama has to say, she is informative in the sense that she gives me topics to go research on my own and is generally helpful.