How we cite our quotes:
His room, a regular human room, only a little on the small side, lay quiet between the four familiar walls. (1.2)
After the transformation, Gregor takes a look at his room. It seems familiar enough, but the expression a "regular human room," a room for humans and not for vermin, suggests that he's already feeling uncomfortable in his own room.
[…] constantly seeing new faces, no relationships that last or get more intimate. (1.4)
Ironically, one of Gregor's main complaints about being a traveling salesman is that he can never establish a lasting relationship with anyone because he's always moving around. Stuck at home over the course of the story, he's still unable to make a connection with anyone.
That's all I'd have to try with my boss; I'd be fired on the spot. Anyway, who knows if that wouldn't be a very good thing for me. If I didn't hold back for my parents' sake, I would have quit long ago. (1.5)
The "that" that Gregor is referring to here is waking up late like the other traveling salesmen. Ironically, that's just what he's doing here, although we don't find out he's late until the next paragraph. Of course, he has a very good reason to be late – he's a vermin. But the transformation has the unintended consequence of fulfilling Gregor's wish to be rid of his job.