I'm so sorry for your loss

When DD1 was a baby we did a 5-6 hour trip (each way) one weekend every month. I quickly learned that the night time driving trick so many people use didn't work well for her at all. She wanted to nurse frequently and was used to being on me that whole time and it was awful. However, she did great if we left shortly before her normal morning nap time. I'd nurse her right before going, and she'd fall asleep in the car not too long into the drive. We'd stop about half way, eat lunch, nurse, etc, and she'd go back to sleep not too long into the second leg of the drive. DH and I got some of our most peaceful alone time during those drives, with DD sleeping in the back.
I'd recommend planning drive time around normal sleep times that aren't regular fussy or cluster feeding times, and be prepared for frequent stops.
Packing plenty of snacks for you so you don't need to stop, and can stop anywhere and not be worried about food could really help. If your little one is really eating solids, snacks for him too. If possible, it may help to have someone ride in the back with him. Music he likes may really help too.
I wish you a peaceful drive.
