I like the idea to donate through NFTs. As a suggestion, I’d add some credibility to your website on how donations get to charities. That would be my first concern when deciding to use your solution.
With ThanX, we are also planning to let users donate their accumulated THANX tokens.
We could work together on that part if you have good relationships with organizations like WWF 
You can check us out here:
Good luck with your project!