I agree you best option is to write up a plan, I applied to sponsor my husband while living in his country unemployed for about a year and a half so I had no income at the time.
I just wrote a plan out for how I plan to support us when I returned. For me, I had to job offers, one from my previous employer, so i showed them my old T4 slips and paycheques. It wasn't a high paying job I had at the time I made 15,000 one year and 13,000 the next because of new management and hours.
So if you can explain how you plan to live off of the 30,000 in your bank for the three years until pension you should be fine. And if your girlfriend does want to work you can say so, you could write about how you have 30,000 and your girlfriend will be looking for a job herself. But if not, I am sure 30,000 well budgeted can last you until pension! Basically explaining anything in a letter that might cause the officer to doubt or ask questions will help them to understand and avoid delays!