I think the ferris wheel is lovely, since you’re doing it at night. Gives a feeling of being apart from the rest of the world for a brief moment…
Marvel said, "I wouldn’t spend the money on one until you were 100% sure of her ring size. "
Any ring can be sized. This is not an issue. Hell, my ring was too big and I WAS THERE when we picked it out!
Why don’t you ask her what she means by formal? Maybe she’s afraid you’ll back out and she wants witnesses. Maybe the ring signifies “formal”. Maybe she wants skywriting. I’d ask her.
Well I sorta want to surprise her. It has been a long, long wait and I want it to be very special for her.
Paul, you know her…if you think she wants the proposal, then she will be ecstatic when it happens. If you have any reservations about the Eye, like that she’ll be nervous from the height, or the “public” nature of it (i.e. strangers around) might make her uncomfortable, then you will know this.
I asked my fiance to marry me twice. The first time, we had just spent the entire christmas vacation together, and we had begun talking about the wedding, even going so far as to choose a first choice for our date. For all intents and purposes, we were engaged. As we were in bed the last night before her having to go back home, we talked about it, and I figured the ambiguity wasn’t so good, and we both knew that getting married was what we wanted. So I told her to sit up on the bed, and I kneeled in front of her, grabbed her hands, and asked her to marry me.
This was private, and not some special thing, but it was the natural conclusion to all the experiences we’d had the preceeding days, and it caught us both off guard, but it was special to us…which is all that matters.
2 months later, I had purchased a ring (after telling her money was too tight and she would have to wait for the ring I wanted to give her) and we went to disney world…her, her parents, and her daughter, and I. So the most important people in her life were there. when you walk into the park, you walk down main street, towards the castle, and there are employees there wtih cameras to take your picture. We had a couple of pictures made, and then I requested one more, just me and my fiance. Right as the guy was about to take the picture I slipped down on one knee, pulled the ring out of my pocket and held it up, and asked again. She was caught off guard (Which is what I wanted) and her dearest loved ones were there, and her parents knew I was gonna do it. I didn’t ask “permission” as much as I let them know, and made sure they didn’t have reservations.
She, I believe was extremely happy with both “engagements” and she was very surprised both times (Hell, I was surprised the first time)
Anyway, my point is, I’m sure you know what will make her happy, and what to do, or not to do. And if you really love her, and she really loves you (as I’m sure is true) then whatever you do will make a wonderful story to tell, and will make her happy. (Unless, you, you know do something really wrong like throw the ring at her in the middle of a fight and scream “FUCK YOU I WAS GONNA ASK YOU TO MARRY ME BUT FUCK YOU”.
That’ll not be a good way for her to find out you wanna ask 
Good luck. You’ll be fine, I know
Steve