A 'secret relationship' trope can be found in many of these fanfictions. Given Thorin's position as a leader and the differences in their backgrounds, they might have to keep their relationship a secret at first. Also, the 'soulmate' trope is popular, where they are somehow fated to be together, which can create a really romantic and engaging story.
A theme that frequently appears is the idea of love and attraction in a new light. In many fanfictions, the relationship between Fem Bilbo and Thorin evolves into a romantic one. But it's not just a simple love story. It's often set against the backdrop of the adventure and the power struggles in Middle - earth. So, it combines elements of action and adventure with the development of their relationship. Also, the theme of self - discovery for Fem Bilbo is common. As she goes on this journey, she learns more about herself and her place in the world.
I also suggest 'Fem Bilbo and Thorin: The Untold Bond'. This fanfiction focuses on the emotional aspect of their relationship. It shows how Fem Bilbo and Thorin slowly come to rely on each other. The story is beautifully written, with detailed descriptions of their feelings. There are many tender moments between them that make this fanfic stand out, and it gives a fresh look at the characters within the 'The Hobbit' universe.
One idea could be a story where they team up to solve a mystery in Middle - earth. Maybe there's a strange magic at work that's causing problems in the Shire and Thorin, with his experience, and Bilbo, with her quick thinking, have to figure it out.
There is a fanfiction called 'Thorin's Treasure'. It delves deep into the emotional bond between Bilbo and Thorin. It shows how they support each other through various challenges in Middle - earth. Additionally, 'A Hobbit's Journey with a Dwarf King' is also quite engaging as it focuses on their shared adventures and the growth of their relationship.
One great bilbo and thorin fanfiction is 'The Road Goes Ever On'. It beautifully captures their evolving relationship during their journey. The author does a wonderful job of portraying Bilbo's growth and Thorin's internal struggles. Another one could be 'A New Alliance'. It focuses on how they work together to face challenges after the main events in the original story, showing their deepening bond.
Love is also a prevalent theme. Whether it's a platonic love or a romantic one, many fanfictions play with the idea of their feelings for each other. Some explore how their different backgrounds, Thorin as a dwarf king and Bilbo as a hobbit, influence the way they express their love and care for one another. It can be a very interesting exploration of their characters' emotions.
Redemption can also be a theme. Thorin's pride and how he might overcome it with Bilbo's help is something seen in some fanfictions. And loyalty, both to each other and to the company they are part of, is frequently a central theme as well. For example, in some stories, they are tested in terms of their loyalty to one another during difficult situations.
Goodreads has some fanfiction groups as well. Some of them might focus on The Hobbit fanfiction. You can post in those groups asking for fem Bilbo and Thorin stories. Additionally, Reddit has subreddits related to The Hobbit and fanfiction. Browse through the posts and comments, or make your own post asking for such fanfics.
One great Thorin Bilbo fanfic is 'A Chance Encounter'. It beautifully captures the growing relationship between them. The author does an excellent job of portraying Thorin's pride and Bilbo's courage in a new light within the story's unique plot. Another is 'Under the Mountain's Shadow' which delves deep into their emotional bond, with vivid descriptions of Middle - earth that make you feel like you're right there with them.
You can try looking on fanfiction.net. There are a lot of great stories about Bilbo and Thorin there that focus on their friendship or adventures without involving pregnancy themes.