Moving home with a 3.5 year old

I am emailing today to ask for your advice. I am the mother of a three year old boy. My son has gone through a lot in this past year including have a tumor (non-malignant) removed from his lung. All my sons life I have lived with my parents for 1. I divorced my sons father while pregnant and had no other place to go and 2. my mother is chronically ill and I take care of her. Why I am emailing and asking for advice with is due to family dysfunction caused by my very unstable and drug addicted sister with three children herself- I find it is time to move. The stress and the fights are not what I want my son growing up in. I myself grew up in this mess and want nothing like this around my son. My son is a very resilient and strong willed child but he is very attached to his grandfather. Why I am emailing is how do I make this move less stressful on my son. How do I effectively communicate why we are moving and our new home will be somewhere else. I am so afraid of doing more damage to my son then if we just stayed unhappy and hurt all the time in this mess at my parents. I am twenty five years old and a single mom it's time for me to separate myself from this mess. My son and I still co sleep and I strongly believe in attachment parenting. I know my son feels loved by me and my parents but how do I facilitate a separation without hurting my son. Any advice you can share would be greatly appreciated. I do not normally reach out ot strangers about my problems but when it comes to my son I will do anything. Thank you for your time.

First I want to tell you how impressed and in awe I am of your bravery and commitment to creating a better life for your son. You should have no doubt that you are making the right decision. Good for you.
Personally, I don’t think your son will have problems with the transition. I think he will know instinctively that it is to create a better life, a prettier life, and will appreciate it as it sounds like the current situation is literally taking his breath away. We respond physically to negative situations and our bodies literally give us indicators of what we are living. If he has already had health problems at his young age, starting a new life in a new home is the best thing for him.
Saying that, introduce the topic to him as an exciting adventure. Talk about the new home, go and see it, and make him part of the process. Talk about what you will do there, what you will bring that he has in the old home, and how you want to create a place that feels nicer. Children understand how places FEEL, so start the journey with that as a focus. When you move, make it as stress free as possible, not worried about his routine, going by his cues regarding setting the place up, eating on cardboard boxes as tables, stopping to play for a bit and then setting things up after he’s gone to sleep. Make it fun and he will go with the flow. He’ll sense that things already feel different, and he will probably relax into it, relieved.
Regarding his grandfather, I’m assuming you are staying in the same area, am I right? If he asks about when he will see your dad, tell him you’ll be having him over and you think it would be nice to have a place for your dad to visit which feels nicer than your parents’ house. Have your father over, or even help with the move if he would. Visit your family once you are set up, so that a new routine is set up. If you can’t then do a Skype visit and let your son show your father around his new house.
On a personal note, I was living at my folks when both our daughters were born. When we left they were young, but had known no other home and I was worried it would shake them and leave a scar. It hasn’t at all, and as long as they had the security of my arms they were fine. Since then, we’ve moved often, each time I’ve wondered how they would deal with it, and as long as we’ve brought what things they cherish, they were fine. Our 3 year old just moved again, this time back to Canada from the UK, and since we set it up as a new adventure, with fun, new things to do, he’s thrived with it, occasionally mentioning things he misses, but eager to do all the things he can over here. Life is about the Now, and as long as we make it a joyful, fun now, our children adapt quickly and are eager for more.