While Naomi has her at home secrets
Later of plenty of things will be optional.
Impregnation is a big theme, it will show in different ways.
I'm sure you have no end of suggestions from paying supporters, but since we're on the topic. If impregnation/pregnancy isn't a required milestone/story beat. . .
Along the lines of optional content.
Dirty talk options that open the door to Naomi's willingness to graduate to MILF? The player choosing these can be an intuitive way to enable impregnation-play after the topics are used enough to pass an invisible threshold. Once passed, condoms can break, Naomi has fertile days, days that she might be willing to risk going without a condom? A little past that, she might be willing to do the raw pull out method?
Possibly some non-sex-scene conversation moments where she could ask him if he was serious, or if he hasn't been creaming her after the dirty talk, for some time, she could tell him that she was serious about it.
If certain debuffs/buffs are in play, she's on top, and if she has an orgasm while the player is within the PC-can-cum range, he'll start to ejaculate before she can hop up/ climb off. Likewise if PC is on top and the same situation happens, perhaps she'll leg-wrap the PC and hold him inside as he follows her over the edge.
Could cause a loss of relationship points ("she's mad") if impregnation willingness is low, and a relationship gain if her willingness is high.
I'd also enjoy something of a reverse situation if love value is very high, impregnation dirty talk was used, but PC has been careful and has kept it as "roleplay" and hasn't been creaming her. Naomi perhaps mentioning it more and more, a notably higher sexual appetite. Asking the player to go in raw if they chose to use a condom, or if she's on top, trying to pull it off if the player doesn't click a "leave it on" chat response?
Could also just include some "flavor" backround details. If they're trying to get her pregnant, the day change graphic could have hearts or lewd doodles (presumably from Naomi, as if left on a calendar?) to signal fertile days. If not a literal calendar hanging in the kitchen with ovulation dates marked up somehow. "Show not tell" details. Or leaving condoms on the coffee table / bedside table when she expects you to use them.
Haven't seen very many good games when it comes to implementing the impregnation fetish and all the niches surrounding it.