I use the large size font - seems pretty good to my (getting older) eyes. Although it would probably be much the same as the 5220. Perhaps have a look at one in a shop?
If you turn the phone sideways, you get a full alpha keyboard. Using the supplied tool makes typing even easier.
Or better still, install the Swype keyboard
http://betalabs.nokia.com/apps/swype-for-symbian.
These don't change the font size though.