Which poem can be compared to Emily Dickinson's "I heard a Fly buzz—when I died—" regarding the theme of death?

Emily Dickinson is my all-time favorite poet, so it is a joy to help you with this question! The poem "I Heard a Fly Buzz—When I died" seems to be focusing on the literal moment of death for the speaker. A poem that I would compare it to in terms of the themes of death and dying would be "I felt a Funeral in my Brain."

In the poem "I felt a Funeral in my Brain," the speaker seems to be at her own funeral, after her death. The speaker comments about the mourners moving "to and fro" in the first stanza and then goes on to describe the funeral service and eulogy in the second stanza. It is almost as if she is watching her own funeral as she states,

A service like a Drum—
kept beating—beating—till I thought
My mind was going numb.

She goes on to discuss the funeral further as the box (presumably the speaker's casket) is lifted. The speaker begins to feel the pull of Space. She sees herself as being "Wrecked solitary here," which is to say she must make this journey alone.

Emily finishes the poem with a line that is quite telling of her own views of death. She says she "Finished knowing then—."

While the two poems each view death and dying from different perspectives—and at different times in the journey from life to the afterlife—I believe the themes coincide quite perfectly. Hopefully this will help!