We had an email recently from LHC member Rose in Austria saying that she had been researching iPhone apps that have a left hand mode and we thought this information might be useful for you as well.
There is a simple calculator called Southpaw on the ios App store that has all the controls on the left for easy tapping.
And we found a big list of IOS apps with a left-handed mode here:
The list of Android apps with a left-handed mode is here
We have not tried all these apps and cannot make any specific recommendations, but we would be very interested to hear what you have used and any you really like. Please add a comment below to let us know.