This 1950s John Calvin bio is an enjoyable, easy read. It's reasonably priced ($5) or available for free download here.
This will probably be the main source I use in presenting a simple biographical message on Calvin in adult Sunday School. There's one anecdote from the book that I'm not sure will come up then so I'll mention it here.
Calvin had lots of young children in his home for many years, meaning his greatest works, like The Institutes of the Christian Religion, were written in the midst of teething toddlers and messy diapers. That a text of this import (it's still a standard in many seminaries) was written in a context like mine is both motivating and deeply depressing. Calvin was one-of-a-kind.