There are several options for printing on cotton. The easiest is to use a heat transfer material to print on, then use a heat press to transfer it to the fabric. These usually like at least a 50-50 cotton/polyester fabric.
Then there are specially treated cotton fabrics--usually with a backer sheet to allow them to feed through the printer.
Then finally, there are the dye sublimation inks, which can be used to print on a transfer material, or directly on to fabrics--again heat activated.
Just do a google search for fabric printing, I'm sure you will find lots of options there!
John Nollendorfs