Tax credits would be part of your universal credit claim now. It’s called the child elemen. So how much you get would be determined by your other income, if that’s only going to be universal credit. You’ll receive the full child element.
You’ll also receive an element for yourself as well as help towards the cost of your rent (unless you own your property) it’ll all be paid as one payment.
As your child is just a baby you won’t be required to look for work yet so if you can afford to live on your payment you can have a bit more time off with the baby if that helps.
The child element is £277 per month. Your element depends on your age. Have a look here:-
Check what benefit entitlement you are entitled to. The entitledto benefits calculator will check which means-tested benefits you may be entitled to e.g. tax credits, universal credit, housing benefit …
www.entitledto.co.uk
Try not to stress, it is a horrible benefit. If you’re struggling go to your local CAB or Welfare Rights Team at your local authority, they might be able to help.