New young mummy needs help!!

So, I'm 21 and partner is 22, we are currently renting through housing but only in a tiny tiny 1 bedroom that isn't really big enough for the both of us. First baby is due middle of December, housing has said they won't move me because I'm not a priority, we can't afford to move elsewhere and rent because we just won't have enough money especially once I stop working (both only casual so never know how many hours we will get a week) and my mum has said we can move back in with her in the downstairs area that has two bedrooms joined with our own bathroom, completely separate from my mum. We would be paying a little board but saving close to $600 a week but my parter just won't think about doing. Says I chose to keep the baby so I have to deal with either staying where we are or moving out and making it work. I honestly think it's best to move back in with my mum, we will have support, save money and won't have the stress of being somewhere we can't afford but every time I bring it up he tells me I'm selfish for even considering that and he won't do it.

Need help or advice or something, I just don't know what to do and I'm getting so stressed about it all.

In Australia by the way