Birth Control???

So I'm almost 17 and have been dating my boyfriend for 4.5 years. We have a really strong relationship that hasn't been physical at all until about a year ago. We are both still virgins but I know we are coming to the point where we are going to want to have sex with each other. We've talked about it, and its not going to be any time soon, only when we both feel comfortable and ready. However, my extremely over-protective mother still cringes when she catches me and my boyfriend holding hands. We have to be so conservative around her its ridiculous! She's a single mom and works late, so she isn't around much of time, but still its a tad frustrating. My boyfriend's mom is a lot more understanding and as even offered to get her son condoms. I would just feel a whole lot better if I had birth control too. I know condoms aren't 100% and I don't want to take the chance. Only problem is, where can I get birth control without my mom knowing? How much would it cost? I've tried doing some research online but I'm wondering if any of you ladies out there have personal thoughts on what works best? I know I could probably talk to my boyfriends mom but I feel like that's so embarrassing:/ I'd rather just get it on my own. I live in Arizona if that helps.