Hi mate.. you need to provide evidence that you have somewhere suitable for you both to live, this would normally mean tenancy agreement or title deeds. If you dont own the property it may also be a good idea to get confirmation from the landlord that it is ok for her to stay there with you..
Unless you have a copy of the tenancy agreement for the new house it wont mean squat. If it was me, i would keep it simple and refer in the application to the address you currently living in and provide evidence relating to that. I think that any suggestion of your outgoings going substantially up is just asking for trouble.
this is just my opinion