Spoiler, though: It's NOT too good to be true! Two of my coworkers also use this same exact mattress and have been perfectly pleased with it. (Read a full review of it here.) It's available in sizes twin through California king — including twin XL, aka the perfect size for dorms — as well as in 6-inch, 8-inch, 10-inch, and 12-inch thickness options. I opted for the 12-inch version, as the thicker the mattress, the softer it typically is (per a Zinus representative's advice).
I'll pretty much echo everything that was mentioned in the review linked above. The mattress is of the bed-in-a-box variety, meaning that once it arrives, you'll need to give it up to 72 hours to totally ~expand~. Mine had completely flattened out within seemingly 15 minutes and I slept on it the same night I unboxed it. Slept like a baby — a type of sleep I have continued to enjoy since. As for those of you who, like me, have a tendency to "sleep hot": I have not felt noticeably hot in the middle of the night to date, but temperatures in New York haven't climbed above 40something overnight, so time will tell on that front, I suppose. But adding a cooling mattress topper is one way to solve that issue.
I'm not entirely/not at all sold on the infusions of green tea extract and charcoal "so you wake up smelling less like sleep and more like fresh" claim — but for a comfortable mattress this cheap, it can claim whatever the hell it wants to, really. The one caveat I would be remiss not to note is the initial smell of the mattress, which took nearly three weeks to fully dissipate BUT which I found oddly coffee-like and pleasant? (My boyfriend would disagree, but idk man, I thought it was kinda comforting.) Could I have circumvented this by cracking a window open for a day? Probably. But it's been too damn cold, and it honestly didn't bother me very much.
Get it from Amazon for $90.99 (twin)–$290.02 (California king).