First, are you saying your tank had no light at all?
I have tanks near windows, and I still put a light over them. A flourescent tube should be fine, in addition to whatever natural light you are describing. Buy a timer (they're cheap) and set the light to be on for 10-12 hours a day.
You will also need a liquid fertiliser, and from what I hear, flourish comprehensive is the best.(I use soil, but flourish is decidedly easier)
For plants, I'd try swords (Echinodorus blehiri, or klienar prinz, or rosette sword), vals,
Java Fern,
Java Moss, and
Anubias first.
May also want to add
Duckweed or azolla. The
Goldfish will probably eat it, but better they eat that than your other plants.
Duckweed grows super fast, I bet they couldn't ever get it all.
For a longer list, track down Lupin on this forum. He's the
Goldfish plant expert. :)