I'm walking on air. 我感到飘飘欲仙。walk on air“洋洋得意”。

A: How do you feel? 你现在感觉如何？
B: I'm walking on air. 我感到飘飘欲仙。

I'm high on life. 我活得很快乐。high在这里是“高兴的，快活的”意思。

A: You look happy every day. 你每天看上去都很快乐。
B: Yes, I'm high on life. 是的，我活得很快乐。

I'm on top of the world. = I'm sitting on top of the world. 我太高兴了。

A: You won the first prize. 你得了一等奖。
B: I'm on top of the world. 我太高兴了。

I'm in a great mood today. 我今天心情很好。

A: I'm in a great mood today. 我今天心情很好。
B: Tell me why. 告诉我为什么。

I've never been this happy as I am now. = This is the happiest moment in my life. = This is the best moment of my life. 我从没有这么高兴过。

This is too good to be true.简直不敢相信有这样的好事。

It's unbelievable. 真难以置信。

I lucked out today. 今天的运气真好。

I'm in luck today.= I feel lucky today. =It's my lucky day.

luck out“运气很好，侥幸成功”

You're to do exactly as you please.= Please do exactly as you please. 你高兴怎么样就怎么样。

I'm in high spirits. = I'm over the moon. 我非常高兴。