You will find a several list of words which are the base of the simple breton. This work is based on these articles:
https://br.wikipedia.org/wiki/Brezhoneg_eeun
https://br.wiktionary.org/wiki/Stagadenn:Brezhoneg_eeun
https://fr.wikipedia.org/wiki/Anglais_basic
https://simple.wikipedia.org/wiki/Wikipedia:Basic_English_alphabetical_wordlist
https://simple.wikipedia.org/wiki/Wikipedia:Basic_English_international_wordlist
https://simple.wikipedia.org/wiki/Wikipedia:Basic_English_combined_wordlist
https://fr.wikipedia.org/wiki/Fran%C3%A7ais_fondamental
http:https://lexiquefle.canalblog.com/archives/2007/06/04/8005581.html