I would get your machine looked at first so you don't have to spend the money if you don't have to. If it does need to be replaced I would definitely upsize. I have a 5.5kg fisher and paykel top loader and it is too small for a family of three. Not looking forward to washing for 4 in it.
I don't think using your baby bonus is a bad idea at all. Exactly what it is for. Helping out when you have a baby not being wasted.