A feeling of gratitude isn't about the amount of stuff. Because it's a feeling it should be filled with feeling.
Obviously my translation of the second sentence is meaningless. How should I translate 気持ち here?
Also I don't understand how こもる works. Apparently it means 'to be filled with' so I would expect 気持ちがこもる to mean 'feeling is filled with ...' rather than 'filled with feeling'. Why is が used rather than で to denote what something is filled with?
For example, in answer to the question "Who is filled with happiness?" how would I say "Tanaka is filled with happiness". I would have said 田中さんが幸せでこもる, but I'm guessing that's completely wrong.