what do I do?

I'm having a hard time being sexy. All my friends refer to me as tiny (I'm 5'4) and cute, even calling me Tomato-chan because I blush at everything. I got into a relationship around last winter and I'm just really shy around him. I had to explain that "sure" means full consent because I'd get too embarrassed to say the word "yes." Even if it's something small, like a kiss. He's been really patient with me, and has learned that if I'm snapping my fingers or bouncing on my toes after he asks for consent, I'm trying to say yes but it won't come out. Luckily he won't do anything unless I say "sure" or can manage to squeak out a "yes".  Recently, he came up with the idea that I should initiate all romantic things. It's supposed to help me say what I want and not be embarrassed. Unfortunately, that's only made me more shy. I want to be all confident and sexy, but I end up giggly and blushing. He mentioned he likes it when I wear lingerie, but I can't bring myself to buy anything because I think I'll look stupid. I can do it in my head, but practical application leaves me red and hiding behind my hair.