Your opening paragraph is a good umbrella statement. It opens the essay firmly by answering the question in short, and then naming the texts that the essay will feature. The structure is needing work though - Try not to break the essay down by same "this text did this" and "this text did that"...
re Rime of the Ancient Mariner
I don't know wether this helps much, but the approch i got told to take to relate it to imaginative journeys is when the ship of death & death herself actually appears in the poem. We know that this cannot happen in real life, hence it is sort of an imaginative...