以下是几种表达感谢的高级英文说法：

Thank you very much.

I'm extremely grateful.

I truly appreciate it.

I cannot express how thankful I am.

I'm deeply indebted to you.

Your kindness is greatly appreciated.

I am most thankful for your help.

Your assistance has been invaluable.

I'm so appreciative of everything you've done.

Your generosity has touched my heart.