I used to be on a medication that made my birth control less effective (not totally ineffective, so I did have some level of protection), so my boyfriend and I chose to use the withdrawal method. It really was in his control, and was a matter of him knowing his body. He never ejaculated inside of me the entire time we practiced that method.

In the past I have also used FAM and used condoms during my fertile window and allowed him to ejaculate inside of me on unfertile days. So that might be an option. But personally, I would probably trust FAM + withdrawal only. Maybe you could just get some Plan B (sometimes you can get it for free/cheap at Planned Parenthood) and keep it on hand in case of an "oops."