If it's only splitting and space is a consideration, that little Estwing fireside friend is pretty neat. The basque axes have short hafts for the weight and split pretty well, but they're not cheap and there have been some reports of recent years having bad heat treats and they are pretty hard to get in the states.
Not sure if CT is still making them, but the saddle axe is a lot of fun for a little axe with one side being a little better at splitting and one for chopping. NOT a dedicated splitter, though, so if you're splitting big rounds, not the choice. It does split a lot better than I thought it would though for how short the handle is, but it might take 2 or 3 attempts whereas a boy's axe could get it with one. But, it adds a decent amount of versatility in a single tool and it's a lot of fun, and fun is important to me when doing activities I do for enjoyment.
The CT woodcraft is a pretty good all-around packable axe. It splits far better than the "forest" axes I've had from Europe, but I don't know if it's really much better than a good boy's axe for splitting. It is a good tool though, IMO. It's a lot better than a thin bitted felling axes or a big machete/chopper, but not as good as a splitting axe or maul by any means.
I feel like a splitting axe might be within what you're looking for, but I don't know of a lot in the smaller size range outside of the gransfors bruk small splitting axe and then you're looking at a lot of money.
What might be an option is getting something like the CT sledge eye splitting maul and cutting the handle down and reshaping the butt or drilling a hole and using a peg or lanyard for a "stop" spot in the handle. I think
FortyTwoBlades
had a video at one point with a cone shaped peg for such a use, when a chopping tool has a straight handle and you need it to not to take an unintended flight through the woods.
Maybe not too helpful, but maybe there are some ideas to work with in there somewhere. I know some people would just use a hammer and wedge in that scenario as well.