Random comments:
.....I would ask why a trike? Despite how sleek trikes look, I'd expect that most everyone would agree that bicycles are generally considerably lighter-weight and faster. There are some like the Tour Easy/Cycle Genius ones that are LWB with upright seating and fairly-low pedals that are easy to balance on. ....Also many trikes have a fixed seat angle; it might be helpful to have a seat that you can change the backrest angle at least somewhat and most touring-style LWB's let you do that.

Also (no matter what you buy) I would suggest an electric motor assist setup. Not because you're old and frail, just because it's really nice to ride in to your destination with minimal effort and arrive with the least amount of sweating. You can charge the battery at work and then ride home using as much or as little assist/sweating as you want.