Hi Aimsmum. For several years we've used the Fertility Awareness Method (FAM) which is NOT the same as the "rhythm" method.
It basically involves taking your temp. every morning and charting it and also taking notice of the state of your cervical mucus. Used properly it is VERY reliable. On the days that I am fertile we use condoms (probably about 7-10 days in each month).
TBH, since having dd2 20mths ago (incidentally, despite the fact that I turned 40 this year, she was conceived within 2mths as I knew exactly when I was ovulating!), I've not bothered with the temp. taking as I've found that checking the mucus is realiable enough on its own, as long as I err on the side of caution (Billings Method).
The book "Taking Charge of your Fertility" by Toni Weschler explains it in detail and it really isn't complex or time-consuming once you've worked out what you're doing.