Thinking about it a bit more, I actually believe that the non-unicycling activity that would best help you get started with unassisted riding would be yoga -preferably yoga classes. Where I live, these classes are sometimes very inexpensive or even free, but that may not be the case where you are.
Balance is closely related to proprioception and flexibility, and yoga brings all three of these things together. It would give you the chance to work on them in a very focused way, without being encumbered by your motorcycle, a skateboard, a 500-pound barbell, a bicycle or even a unicycle. The minimalism of yoga is partly what unicycling is about, at least at the beginning. That’s why, once you get riding around, you will hear so many people shout “Where’s your other wheel?” “What happened to the rest of your bike?” and so on.
The connection (or not) between yoga and unicycling was discussed here a couple of years ago. A friend of mine ended up bedridden for two weeks from some sort of yoga injury, but a few people always manage to get injured doing just about anything! In my opinion, yoga is pretty safe. Of course, there are many different versions of it, and I have no idea what might be available in your area, but Bikram or some other kind of yoga with lots of one-legged balance poses might be extra-helpful for unicycling. In Korean, the word for unicycle literally means “one-legged bike,” or so I was told.
Of course, if you keep trying to ride unassisted, you will probably figure it out very soon anyway, yoga or no yoga.