1. I'm a little worried that you're more into having a relationship than you are with having a relationship with her. Some people have a higher need for physical closeness than others (like myself), but you shouldn't date someone just to fulfill that. If her friendship means a lot to you and you think that it wouldn't be the best idea to try to take things to the next level with her, then don't.
2. On the other hand, if you're worried that she might not be over her ex, just talk to her about. It should be okay to just ask her about something like that if the two of you are good friends.
If you still have the green light after you've considered 1 and executed 2, then I say go for it. Just start of a bit slow. Do more date-like things together with just the two of you if you don't already, and flirt a bit if you don't already. Then when you see an opportunity, ask her if she would like to be more.
(As for your friendship worries, I think that if she's truly your friend, she'll stay that. In my experience, when a romantic relationship with someone who was a close friend first ends, or when romantic feelings are confessed and unrequited, but both people are mature and care about each other, then there needs to be a break at some point for healing but it doesn't have to ruin the friendship. Some people firmly believe that you cant be friends with exes, but I have to disagree if you were friends prior to dating.)
I hope I was helpful and please let me know how it goes!