Are you willing to spend some time on a train? Then, you simply cannot miss with the following:
Thai Elephant Conservation Center
I took their Three-Day Course and it was beyond description.
One thing to watch out for: the mahouts have a phrase to make the elephants de-trunk water... straight at the farangs. Think it was "zoom zoom!" By necessity the elephant's trunk is close to you... if you are quick you can grab the end of the trunk and point it back at the "prankster" mahouts.
But, really, this is a once-in-a-lifetime experience.
YouTube has a series from the camp.
This darling is my one and only True Thai Love.