Sorry to hear this news Jo, but my best wishes...
Here is what I did in similar circumstances
A year or three back I broke my left hand, and it was a bad one, operated on, with a titanium plate inserted to hold the various broken bits together. I was told not to ride for at least thirteen weeks, however I'm completely mad, so after three weeks or so, just like fboab, I also borrowed Auntie Helen's 'spare' Trice Q, recumbent tadpole trike.... (Immediately after fboab, as I recall). Once again my great thanks to AH.
It got me round one of postie's 200s with an hour in hand...
I was able to ride it all the way with my left arm comfortably immobilised in a sling, because it had been modified to have both brakes and both gear change controls on the right steerer handle bar....
It was easy to ride, slower going up hills, (but with an amazingly low gear) and faster going down, but I found the hardest part was getting in and out, and of course moving it around when not sitting in it (being effectively one handed). However that was because I was riding alone, and IF you had someone with you, they could hold it still, and haul you out, or lower you into it, so those problems could be overcome.
Postie's ride was by no means flat, but I still got round, and as I had only ridden the Trice Q on two occasions, my legs were NOT used to it. If you were riding somewhere flat, it would be certainly fast enough.
I am not sure whether this one might still be available, but maybe there is one out there that could be lent to you and have all the controls bunched on one side?
If you can get one, and need a 'possee' member, I would be pleased to ride with you, and I bet there would be others too....
Good luck
Mikey