I might be missing something, but...
Why wouldn't you consider renting? Why the importance placed on saving up for a house deposit? I understand the urge to have a place that belongs to you, but once interest rates rise back to more typical levels you will be paying at least as much in interest on the mortgage as you would do in rent. Anything that you pay off the capital of the mortgage will be additional to this. You could just as easily rent and pay into a savings account as have a mortgage.
I can understand if living with her parents is your only option, in that you can't afford to rent, but living with them just to save up money seems a little odd.
Anyway, my advice would be to find a nice small place; a flat or a small semi, and move in now. If it doesn't work out, then you can always go back to your respective parents. At 23 it is to be expected you won't be earning a massive salary. This will improve as you get older and you progress in your career.