If you're using an orthographic (the tk2dCamera is orthographic) camera, you can simply move the tilemap way back in z. That will ensure it gets drawn before everything else. You can increase the far z plane on your camera if it isn't sufficient.
The character should appear closest to the camera, so you'd want to keep that on a close z distance from the camera.
That should be sufficient to get this working. There are other methods to get this working, multiple cameras, material draw order and so on, but this by far requires the least work.