When I learned to ride a motorbike, the system was that you had to have your bike delivered to a training centre (bascally a playground with cones etc). You were not taken out on the roads for training until you could ride in a straight line, around a series of cones, and weave in and out of them (without falling off or having to put a foot down!)
It sounds like a similar idea might be useful for you (you have suggested this yourself). If you can't find a course, find an empty car park and challenge yourself to (for example) ride along the white lines, or some other challenge. Get a bit more confidence in riding the bike before you try riding in traffic again.
And good luck with it.