Miss Benson's Beetle by Rachel Joyce about a spinster schoolteacher, Margery Benson, who abandons her life in 1950s London to search for a mythical golden beetle in New Caledonia^
Rachel Joyce also wrote The Unlikely Pilgrimage of Harold Fry ...which is also quirky and funny. about Harold who goes on a long journey
...neither of these is relentlessly humorous but both are ultimately "smiling' sort of books - but also with very funny parts.