pretty much any fluorescent tube that's not an actinic will grow plants fine...especially when you're sticking to low light, easy plants. So yeah, pretty much stick to a bulb of the right length, diameter (not as important, espeically if your ballast isn't junky, it'll power several T-sizes).
Your biggest concern should be the color of the light and how it makes the fish look. many plant tubes are very pink/purple, and seem dim to the human eye. if you want a whiter light, look for a daylight bulb.
I would just go to a home depot/ace hardware...you can get an appropriate bulb for about $5...prolly cheaper than any wholesale 'aquarium specific' bulb...they usually start at $12.99 retail and work up.
Former advisor and planted tank geek...life's moved on though.