Sons father, please I need advice!

Stacey
So I'll try to make this short...(a little background) I have a 4 and a half year old son who hasn't seen his biological dad in a year. He's spoken to him on the phone maybe 4-5 times within that period but his dad moved two hours away into his moms house with his girlfriend and their son. He has not paid child support in two years. His father has a history of drug abuse and tickets. Not a superb guy. 
I have full physical custody and I'm married to an amazing man who is raising my son like his own. My parents have been a huge part of my sons life and see him at least once a week. I have been losing sleep over this question....if for some reason I died, what would happen to my son? Would he get ripped away from all that he knows to live in a two bedroom apartment with 6 people?? Would my husband ever be able to see him again? I know my ex wouldn't make trips down here for my son to see my family because he has a suspended license. I was told to write a will, but even then he would automatically go to his biological father until the judge decided otherwise. I asked his biological father if he would sign over rights to my husband and he said no. I am losing sleep over this, i am so afraid and it makes me sick to think if God forbid something happened to me he'll be torn away from all these people that love him to live with people he doesn't even know. Is there a way around this?? Any advice?