well I've got a few suggestions
Your prob already planning on adding this but just in case I would suggest a lot more scenes with all the girls.
In terms of gameplay mechanics, I think a dart trap would make a good addition and maybe they have an option to laced with something from one of the girls.
An oil trap might also work, it could easily be paired with the fire trap which the hero will take more dmg or could give a boost to the tentacle trap making it so the hero will stay in it longer
maybe have a minion roaming the halls like a slime that could tie into another trap like the tentacle one, the slime could be similar to gas where it stays on you and adds dmg to other traps or could act as a possible mine where once the hero gets into a trap it activates in some way that will make the hero take more dmg or give them a stronger scent so it ties in with one of the girls
A minion to reset a previous trap after the hero falls through the trap door
a net or web trap could be used like gas so the hero takes more damage or make it harder for them to get out of other traps so they take more dmg or it could lead to special scenes with the girls where they find the hero and it leads to something else, and it could tie into the girl that deals with strings
In terms of new girls, someone mentioned a tentacle-based girl I agree with that idea, but I would like to suggest a more muscular girl and maybe a slime girl