Hi Judy. I use a foley & leg bag. I'm paralyzed chest down for 25yrs.
First off, balloon's job (for men anyway) is to keep foley from pulling out, not for sealing. Balloon gets inflated inside bladder not urethra creating a large water balloon you can't pass.

Foleys come in gauges which is word for diameter, from pasta size to pencil thickness. What's the numbers on your foley wrapper? Example 18F is 18gauge which I use.

Once a month?? Not me. Once a week at most. Plus balloon loses approx 1/5th of its water by then (my brand cath's anyway).

Wrapper states balloon on mine to be inflated 10cc's, I only 6cc cause it's plenty & afraid of it popping.

Let's start with what size you have & you're not the 1st woman to tell me it leaks.
Ed

edit- "gauge" was probably wrong word cause higher gauge #'s usually mean smaller not larger as in needles & wire. Larger # for foley = larger diameter though for sure. Sorry!