Another theme might be the relationship between Snape and the other characters in the context of being a single mother. For instance, how would the students react? Would they be more empathetic towards him? And also, how would his former enemies or friends, like the Marauders' friends or Dumbledore, interact with him in this new role? There could be a lot of character - development - related themes.
I'm not sure about specific 'snape is a single mother fanfiction' titles offhand. You could try searching on fanfiction - specific websites like Archive of Our Own (AO3). They have a vast collection of fan - created stories, and you can use the search function to look for ones related to Snape in this rather unique role.
One possible theme could be the contrast between the innocence of the Teletubbies and the often dark and brooding nature of Snape. It could be about how Snape reacts to the simple and happy world of the Teletubbies.
The theme of dealing with society's judgment is also very common. People in the fanfiction might look down on Bella for being a single mother, and she has to find ways to rise above that. She has to be strong for her child and show that she can provide a loving and stable home environment despite the negative opinions of others.
One common theme is self - reliance. Hermione has to rely on herself to raise her child, like finding a job, a place to live, etc. Another theme is the support of friends. Often, her friends play a big role in helping her through the tough times.
Love and loyalty. Snape's love for Lily was unwavering, and his loyalty to her memory could be a central theme. He 'goes the distance' in his loyalty, which could be explored in terms of his actions at Hogwarts to protect Harry.
One possible theme could be discipline. In the fanfiction, Snape might see Harry as needing strict guidance and uses the whipping as an extreme form of discipline, perhaps to teach Harry a lesson about the dangerous world of magic he's in. Another theme could be power dynamics. Snape has a certain amount of power as a teacher, and the act of whipping Harry could be a way to show how that power can be misused or used for what Snape believes is Harry's own good.
One possible theme could be redemption. Snape, who has a complex past, might see Hermione as a way to redeem himself. Maybe he realizes her intelligence and potential and wants to guide her in a different way than he does with other students.
One possible theme could be about breaking boundaries. In the context of the normal relationship between Harry and Snape in the original series, this fanfiction concept might be about going beyond the expected and exploring a relationship that defies the norms. Another theme could be about power dynamics, with Harry perhaps being in a submissive role in relation to Snape, which is a complete reversal of their normal dynamic in the books.
A theme could be redemption. Perhaps Snape has done something so unforgivable in the eyes of Harry that it makes Harry think Snape sucks. And the story could be about Snape trying to redeem himself in Harry's eyes. Or it could be about jealousy. Snape may be jealous of Harry's fame and Harry may sense this and thus dislike Snape.
One possible theme could be redemption. Maybe James realizes the wrongs he did to Snape and the kiss is a sign of his attempt to make amends. Another theme could be a change in their relationship dynamics, from enemies to something more complex. For example, a sudden realization of a deeper connection.