The only thing I've seen (it was featured on the ABC television program "The New Inventers" many years ago) was a trike set up for a young boy that was in the same predicament as yourself. The trike was a recumbent design with a bucket-style seat which, when the cyclist leant one side or the other, would cause the trike to steer in that direction. I do not recall how braking or gearing worked. Maybe that's a starting-point… have a look at who sells recumbent trikes in your area, then see if the set-up can be adapted.
As hand-signals are pretty much an impossibility, you'd probably want to consider some sort of bicycle indicator system. LED indicators for motorcycles work quite well for this, just needing a simple circuit consisting of a few switches, a NE555 (and supporting passive components) and a power MOSFET to blink the indicators. I have such a set up on mine (noting that I have no physical disabilities, I just prefer not taking my hands off the handlebars) and it has been working quite well for some time.
https://hackaday.io/project/19436-bi...ighting-system
Good on you for wanting to give it a go though. I wish you all the best.