If you want a baby, get a baby, as long as it is least old enough to have eaten consistently a bunch of times.
Lots of babies really are fine in tanks that size. But they need lots of cover, not a lot of open space. So, hides, boxes, tubes, fake foliage, branches, piles of moss, etc. And cover the back and sides with paper, maybe like a decorative background if you want. Yes, it will be an adjustment for a little guy who's used to a dark show box, but they can adjust. There are a lot of threads about underweight being rescued and rehabilitated after being kept in a tank with a water bowl and a hide and nothing else (and an uncovered screen top that lets all the humidity out, and no idea what the temp and humidity actually were). But a tank with correct temps and humidity plenty of places to hide and get around without having to cross open ground, etc, is not the same thing at all. It doesn't have to be expensive.