can someone tell me a website or help me write a letter of agreement?

me and my husband been together 10 years but we havent been in our best terms for about 2 years..we both decided to live separately but idk what can happened after we live separately..we dont want a divorce right now..we just need our space..so i decided to make a letter of agreement and get it notarized and also add a witness..but idk exactly what to put on there..any suggestions?