Your needs are limited and your data will never grow to large volumes (can you actually forecast that now?)
You are unable to acquire the methodology of database construction. You may however consider either outsourcing this task to someone else or using simpler tools.
You use complicated spreadsheets and you lack time or money to switch to databases. Think or ask someone whether this does not lead down a blind alley. Don't count on magical tools that would change your spreadsheet (regardless how well made) into a database.
Your data collection expands every week.
You often create new spreadsheets, copy within these and you feel that this work is getting more and more tedious. In this case the effort of switching to databases easily pays off.
You create reports and statements for which the table view of a spreadsheet is not suitable. You can then consider switch to using a database with form views.