I'm not currently married, and do not (currently) want any more kids.
My current girlfriend is young - 24. And she doesn't take the pill. So I use condoms. Except that she uses a natural fertility computer religiously, and swears by it.
It's either this: www.amazon.co.uk/Uebe-0630-Cyclotest-Temperature-Fertility/dp/B001F7FXP4
Or this:
www.lady-comp.com/
I don't think I'm fully comfortable with the idea yet....