While he was listening in, he decided to work on something else. Jeff found it cozy in there, and decided he wanted to alter reality so that this was where he was normally; His actual home, complete with modifications to accommodate him. He didn't tell Emily this, however; Since reality was being altered, she'd be adjusted to think it was normal.
He was writing down everything he wanted. For one, her womb would be bigger on the inside than on the outside, allowing him to comfortably move around. He also set it so that the internal walls were softer, and more flexible, with a house made out of them present inside; This would not impact impregnation, and through the front windows he'd even be able to watch and give updates on a baby growing.
Everything would automatically be furnished, and he'd also be able to leave if he wanted to. Jeff also wanted to make it make sense with the new timeline, however; So, he gave all females the ability to do unbirth, but it would rarely be done, especially to the extreme of Jeff's situation.
As to why he's in there, he decided to put in that due to their close bond, she allowed him to live inside of her womb; The friendship they had was already tight, so the main thing that changed is her permission to stay there rent-free. Her family is mostly aware, except for her younger siblings, who would remain too young to know about this.
As an extra detail, he decided to make it so that only few families have houses inside their wombs, with fewer actually knowing about the detail. Emily would be one of the only ones to truly know, due to Jeff living inside of her, however a good portion of her bloodline would carry it, including her siblings and cousins.
As a quality of life detail, he added that electricity would be available in the wombs of any girls who have this internal feature, generated directly by their bodies in an infinite supply. This way, he'd be capable of charging his various devices without having to leave. For another QoL detail, he decided to have fun, and put that anyone inside could walk on the walls without issue, and beyond that, gravity would be mostly normal; This way he wouldn't be flung around as she leans, and neither would any of his furniture.
With all of this set up, he adjusted his position in the tiny womb slightly, and then hit confirm. The world around him faded away, as he entered the new one...
The next thing he knew, he woke up in his new room. It was certainly a lot cleaner in there, and the walls were actually painted, to his surprise. "I don't remember setting that..." He decided to look around his new place. There were bathrooms around the place, although no toilets from what he could see, and the kitchen had a good supply of food and beverages in it.
From what he could tell, it was effectively a generic house in there, except the floor and walls were all softer. Everything he'd need was in there, inside of his best friend's womb. His main question though was... Why didn't he even see a single toilet?
That wasn't his concern at the moment though, he knew he'd get to that later...