You can say
1) "Thank you with all my heart" (More normal but VERY emphatic. If you're not very serious and extremely thankful it can appear to be insincere)
2) "Thank you from the bottom of my heart" (You can use this, but its kind of an odd expression)
In general, you drop the "I" in expressions of gratitude that use "thank". Its strangely formal, even in writing. However you can say "I greatly appreciate..." where ... is whatever you appreciate (e.g. 'your help', 'the gesture' etc).