I think you are looking at a couple of real options:
1) get your vision sorted out with "gauge reader" inserts (which stick to the inside of your current mask), custom prescription mask or contact lenses
2) buy a diving computer with a larger display - unfortunately for you most of these come with a heftier price tag but are infinitely more readable than a standard button type (such as a console unit). One of the main differences is between LCD (think black on grey) and LED (with multi colour displays).
There are a number of computers with similar size of screens available such as Shearwater, Mares, Suunto, etc. A lot of them have additional features such as compasses & configurable screens as well as optional air integration (which can mean being able to get rid of a hose and the console). I went down the route of buying a Shearwater Petrel and have never regretted it - the visibility in all conditions (low vis, night dives, bright sunlight) is hard to beat and it has allowed me to get rid of the depth gauge, compass and SPG..