1. Add preg content that won't punish you for having sex too much and getting preg
2. Make your first 2 kids fight for you the rest are hostile to save game performance if you must
3. Make sure your sex game doesn't punish you for sex
4. Add the typical tropes like the devs did in sayahatas that conform to your game setting and improve or expand on them
Add bugs that get you filled w eggs like spiders
Add strange tentacle monsters and plant creatures, whatever fits
But keep it unique and incentivize the player to explore sex w diff enemies to have the ultimate companion or other incentives, why have sex in a game if there is no mechanical incentive to do so, gosh I hate how sayahatas incentivizes not to have sex too much when people download it to see sex.
Suggestion over.