Is there a way to say "I respectfully thank you" to familiar elders?

Question

From here.

Honorific Verbs

Like nouns and proper nouns, some Chinese verbs can also be complemented with an honorific modifier. For example, the verbs 告gào ("to tell"), 还huán ("to return")，陪péi ("to accompany"), 劝quàn ("to urge")，送sòng ("to gift") can be complemented by the honorific prefix 奉fèng~ (Lit. to offer respectfully) to form the more polite versions 奉告 (I respectfully tell you), 奉还 (I respectfully return to you), 奉陪 (I respectfully accompany you), 奉劝 (I respectfully urge you), and 奉送 (I respectfully gift you). Another example is the honorific prefix 恭gōng~ (Lit. "look forward to respectfully"), e.g., 恭贺 (I respectfully congratulate you), 恭候 (I respectfully await you), 恭请 (I respectfully invite you)，恭迎 (I respectfully welcome you). The addition of the honorific prefix turns these verbs into a politer version. Unlike adverbs, the prefixes are often verbs themselves, and the compounded honorific verb functions as a single language unit (i.e., a single verb). Other common prefixes for verbs and verb examples are summarized in the verb complements section below.

Is there a way to say "I respectfully thank you"? I've always feared that 谢谢你 was too casual for elders. And 我感谢你 too awkward to say to elders that are "basically family"?

Answer 1

谢谢 is formal enough, the casual thing in the phrase "谢谢你" is '你'. To show respect, you can replace '你' with formal/polite pronoun like 閣下.

To show respect when you thanks someone, simply address that person by his or her title instead of the pronoun '你' (you)

Example:

谢谢岳父 (Thank you, father-in-law)

谢谢老師 (Thank you, teacher)

谢谢总理 (Thank you, Prime Minister)

谢谢夫人 (Thank you, Madam)

You can add honorific like '大人' after the title if the person is an authority figure or with high social status

Example:

谢谢总理大人 (Thank you, great Prime Minister)

谢谢总理閣下 (Thank you, Prime Minister, the respected one)

閣下 is a polite /formal form of pronoun 你; it is also an honorific itself. Only use it with people you are not very close to.

谢谢岳父大人 (Thank you great father-in-law)

To show your humbleness you can also use praise words after the thank you

Example:

谢谢你的大恩大德 (thank you, for your great grace)

谢谢你的再造之恩 (thank you, for your life saving grace)

谢谢你的海量汪涵 (thank you, for your great forgiveness)

Answer 2

You could say 谢谢您 instead.

When you really want to be super respectful, especially to some respected person who you are not quite familar with, you could go with the following

承蒙关照，不胜感激。

厚情盛意，应接不遑，切谢切谢

感荷高情，非言语所能鸣谢

There are many more here which you can check out.