Hi!You can say : fico-lhe muito agradecido or fico-lhe grato. hope it helps!

Agradeceria... Ficaria agradecido. Grato (a) (in writing). These are the closest expressions for that in Brazil. We could translate these expressions literally but would not mean the same, and would sound awkward. Muito obrigado is the most common expression and you can say 'valeu' in an informal setting.

eu apreciei ... eu apreciei muito ... sou grato ... sou muito grato ...

I'm grateful: "Muito obrigado".