Soyuz was apparently considered, but the Columbia orbit was really difficult to get to from the cosmodrome. I don't remember if it just wasn't possible, or if it just would've taken even longer to get ready than the Atlantis. There was an Ariane considered too apparently, just to get some more CO2 scrubbers up there to buy more time, but that would've inovolved developing a completely new packaging and delivery system or something like that. I don't remember the specifics but it wasn't feasible either.
Say what you want about NASA's competence, but you can at the very least assume that if random internet commentators can come up with an idea, then the highly educated rocket scientists at NASA probably could have as well, and if the mission in the report was presented, there's a pretty good chance that it was because that was actually the most likely one to succeed (however unlikely it actually was). Unless you think that random internet commentators are actually smarter than the collective wisdom of everyone NASA has or could have contacted when doing this report after the fact.
Ultimately, I'm not entirely convinced that the "let them have a great mission and then maybe get killed in seconds on re-entry rather than force them to have a crappy terrifying mission and die slowly from CO2 poisoning over the course of several days" wouldn't have been, ultimately, the right choice, even if it was only made by omission rather than officially. I know that if I was an astronaut, I'd choose the former.