I don't have too much in the way of monetary advice except my wife and I found it useful to withdraw our allotted amount of cash each week, and when it is gone - too bad. It made us really think hard about what we were spending money on (especially food). You can always cut corners.
Also, as I think has been mentioned - look at which costs are fixed (like rent - at least once you have moved in), and which are variable. For example, if you put on more clothes, you might not have to turn the heater on (as you can see, I'm not located anywhere near you, so that might not be a reasonable thing, but hopefully you see what I mean). Food is obviously an easy one to save money on - become one of those people in the supermarket comparing prices on everything!
Also on food - buying the biggest container of
product X is not necessarily the most economical - take a calculator shopping and work out the price per kilogram/pound.
Think about getting a smaller/cheaper to run car (says the guy who drives a japanese 4 cylinder).
I'm in the software business as well. Just remember that you haven't sold anything yet, and for your planning you should look at any royalties as "blue sky" (great to have but you cannot rely on it). When you have sold 4 million copies, then you can factor it in - and maybe give us all a loan
Lastly - a bit of non-financial advice. My first wife and I rented a one bedroom apartment just after we were married, and I think the lack of space contributed to our eventual break up. I would seriously consider whether a smaller apartment, which may be good for financial reasons, is a good thing for your relationship.