I have a twin/single from ikea that I got DD when she was 2 1/2 (shes almost 3, so shes been sleeping in it for a half a year). It was pretty cheap, and its close to the ground incase she falls out, which she only has twice. Shes slept SO much better since she has a bed that size, and not a toddler bed.. She woke up constantly in that.
Its is a LOT more sturdy looking in person. I also saw a lot of other beds like that but a bit more pricey. Im a tall girl, with a fairly big frame (not like.. extremely obese, but i didnt think i would fit on the bed haha), and i can lie on the bed with LO and even have someone sit at the end of the bed, and it still holds up lol