if you need a free one,then the latest version of gui launcher collection for kindle touch has nano- a text editor.you need gui launcher installed first.here is the link for the wiki,go to the gui launcher section and download the version according to your firmware:
http://https://wiki.mobileread.com/wi..._Touch_Hacking and here is the link for gui launcher collection which includes the text editor:
https://www.mobileread.com/forums/sho...d.php?t=185562