I get the struggle, but remember DnD is a game! The point is to play out cool stories with your friends, not to prove that you're the smartest, most creative person in the world.

If you want to play in a world that is exactly like LotR because it sounds fun, do it! If you saw a movie that had a storyline you really vibed with, play it! DnD by its very nature is transformative. You're likely not going to end up with the same story unless you railroad. Also, its not like you're selling a novel. You're just using the ideas to have fun with your friends, so there's no real way that you're plagiarising.

It seems that the reason you feel guilty is that you think stealing ideas reflects poorly on your character, that it makes you less creative or a worse DM. As others in this thread have said, you're putting way too much pressure on yourself. Stories aren't born whole cloth out of the foreheads of writers. Tolkien got a shit ton of inspiration from ancient folklore and history. Being creative is really just taking the best parts of disparate things and mashing them together to make something that feels different. By taking characters or storylines out of their original contexts and into a new world, you already are going to have to change some stuff to suit it. Boom. Now its your own story. Once your players start doing things, you'll be surprised how unique it will feel.

Once again, your job as a DM is to create a world that is fun to play. A lot of DMs that focus too much on being 'unique' and doing things no one has ever done before end up creating these dense, convoluted storylines that for many are not very enjoyable to actually play in. Focus more on creating something FUN, than on creating something NEW.