However, you can express varying degrees of willingness using other adverbs or phrases:
More Willingly:
* More readily
* More eagerly
* With greater enthusiasm
* More readily
* More wholeheartedly
Most Willingly:
* Most eagerly
* With the greatest enthusiasm
* Most readily
* Most wholeheartedly
You can also use phrases like:
* Very willingly
* Extremely willingly
* Without hesitation
* With a great deal of willingness
The specific phrase you choose will depend on the context and the nuance you want to express.