Sleep training a toddler

Hi everyone!

I need some help and guidance, so any suggestions are greatly appreciated. My son and I cosleep, he will be 4 in March. He wont sleep unless I am laying down with him. We still need to co sleep but I would like for him to learn to fall asleep on his own. If I step out he cries.

We still need to cosleep because our room just has 1 bed. I rent a very small bedroom so there is literally room for only 1 bed. We share a full size bed.

So how can I give him comfort and security so he learns to fall asleep without needing me beside him. He has a favorite blanket and we already have a bedtime routine established. Sometimes I try to step out for a few minutes. I will say "I have to go pee I will be back in a few minutes" I stay out a few minutes and then he just starts yelling "mom mom mom". Sometimes he will cry.

Ive noticed he really needs to have the security of me not leaving. If I dont have my pjs on yet he will say "mom go change" or if i decide to sit on the bed instead of lay down he says "lay down mom" if i dont cover myself with the blanket he says "cover yourself mom". So ive noticed, that if I have all these thinga done, then he will lay down comfortably otherwise he will not.

Not sure if this background will help, but I went through PPD so I was very emotionally distant the first 2 years. His father and I are also divorced. He has his own bedroom at his dads house but he cosleeps with dad. He is also okay with sleeping over at grandma's house (his dad's mom). But when it comes to my parents (we live with them) he wont sleep with my mom. Im not sure if he just relates the bedroom to it just being him & I. So my mom and sister wont try putting him to bed bcus he will cry.

Thank you everyone!!!!