Moms who used to cosleep

Am

So I have a family of 5 almost 6. I have 3 kids, 9, almost 8 and 19 months. I’m due in less than a month with my fourth. I live in a tiny apartment right now, and resigned my lease in June of last year until September of this year. Before I knew I was pregnant again. There’s 2 rooms so my older two have the master bedroom. Me my, SO and my 19 month old share the smaller room. Well he has been sleeping in our bed, idk what happen because he was fine in his crib until we switched rooms with the kids. I don’t mind Co sleeping but I have a small bed and don’t have the money to buy a bigger bed for all of us (me, the new born, SO, and 19 month old) I feel like I have tried everything to get him back into his own bed and nothing has worked. I would love some suggestions.