One popular Goku and Chi - Chi fanfiction is 'A Day in the Life'. It shows their daily interactions in a very sweet way. Another one could be 'The Training of Gohan', which also features their relationship as parents and as a couple in the story.
Well, 'The Anniversary' is a wonderful Goku and Chi - Chi fanfiction. It's about their anniversary and how Goku tries to make it special for Chi - Chi despite his cluelessness at times. There are also fanfictions that explore their early days of courtship, like 'The First Meeting'. These fanfictions are great for those who want to see more of their relationship outside of the main anime story.
There's a fanfiction titled 'Chi - Chi's Concerns'. It delves into Chi - Chi's feelings about Goku always being away for battles and training. It's really interesting as it gives a deep look into her character and how their relationship is affected by Goku's Saiyan nature. In addition, 'Goku's Homecoming' is a great one that focuses on the warm reception Goku gets from Chi - Chi every time he returns.