Guys, thank you so much for your replies! I even got a few DMs offering to collaborate, so thank you for that too!
I actually went for the A.I.-route, as it made me curious, and I'm really surprised and impressed by it. So thanks for sharing that idea! This might be my favorite approach for now, as it gives instant response, output and gratification. It needs tweaking and often a few tries but there's a playful, almost game-like element that comes along with it. I feel like it really opens up a lot of possibilities and it's really interesting to see what certain inputs can lead to. I think it has it's limits and works better for certain stories than others but so far I'm really enjoying it and I'm actually in the process of finishing up an A.I.-assisted story right now. I will definitely post it once it's finalized!
I also snooped a bit around on fiverr and even contacted two writers, but so far it hasn't lead to anything concrete yet. Is there a writer you particularly recommend (for example out of the list of links you posted), @bloox? But I know this is a trial and error thing too, of course. You probably have to find the right author for the right story. But it is very good to know that this option exist (I knew of fiverr before but somehow never thought about looking up erotica writers there)! I think I will commission something sooner or later. Just want to make sure to find someone I can be sure about first and not waste any money.