Gabriela, there are a lot of great discussions on condoms on this site from a couple of years ago. There is a Japanese brand, called Crown Skinless Skin: http://crownskinlessskincondomss.wordpress.com/ that I've been using for a long time. They are super thin, very strong and non-lubricated. You can use it with Matia's lubricant or just plain Jojoba oil.

A really great book about charting your cycles is "Take charge of Your Fertility" by Toni Wechsler