"I would like to use different expressions to say that." It's not necessary. The phrase "you're right" is ALWAYS good. I do not think non-native speakers should deliberately try to add idioms or colloquialisms, but if you enjoy knowing about them... [Nod and not say anything] [Not and grunt "Uh-huh."] "Yes." "Indeed." "I see." "I get it." "That's true." "That's so." "Isn't that true!" (Rarely: "Ain't that the truth?") "Isn't that so!" (Rarely: "Ain't that so!") "You bet." "I agree." "You said it." "I couldn't agree more." These might be regional, or dated, or simply colorful expressions of individual personality--but these are common: "You hit the nail on the head." "You can say that again." "Well said." "Amen, brother." "Hear, hear!" I am not sure if these are in consciously patterned on Spanish, but I've heard both of these expressions used, more than once, by native English speakers who just like the phrases: "So it is." "You have the reason."

"that's correct", "I couldn't agree with you more", "absolutely", "why didn't I think of that", "that's just what I was thinking"

Sometimes I just say "absolutely!" or "indeed!" It works in situations such as this: "I think that meeting was useless. We didn't decide anything at all! We should've stayed at home!" "Absolutely!" (You're right/ I agree/ You're absolutely right) Mind you, you could always just say, "Yes."

You could say 'That's true' or 'I agree with you'.