Sleeping arrangements

We have my almost 4mo sleeping in a graco pack n play every night. He always bangs his legs on the mat and so we've started bringing him into bed with us. Now, I'm convinced he likes the softer bed better than his own (not just being next to me). I can't get him to sleep, but he'll happily sleep on the couch during the day or the bed by himself. I want to either buy a pack n play mattress or something... Until we can afford it, do you think it would be a bad idea to stuff his bed with blankets? I'm worried about sids still, but he (and his parents!) are desperate for sleep.. Any ideas would be helpful!!. 😴😥😴