asking for birth control

Okay so I'm about to be 16 and my boyfriend is 18. We've been together for two years and we're thinking about sex. I know what your all thinking... "your too young" but I'm physically and mentally ready for it. He treats me right and has always respected my body. Another thing is when we have sex, I want him to wear a condom while I am taking the pill or shot (whatever my doctor recommends). This way if the condom breaks I have something to fall back on, plus reducing the risk of any disease. So here's the real question. How am I supposed to ask my mom? She's has always been on the strict side but she might understand. I'm just not sure how to approach it. I'm not going to have sex until I'm 16 but I want to ask her soon so we can discuss the different types of birth control. I just need some ideas on how to ask her. I'm just nervous.