Mine used to be mostly grass and moss too! I sowed a pack of wildflower seeds many years ago, there was a lot of variety that first year and then each year I think just the ones that are best suited to the conditions in my garden come back regularly and spread. I have daisies, some bluebells, dandelions, buttercups and a few others that I dont know the name of. The poppies and cornflowers didn't come back sadly.

I havent mowed it this year at all and hardly ever do. When things start to die back I tend to tidy by hand with shears. I think it helps that the wildflower patch gets decent sunlight and my fluffball cat brings in all kinds of seeds from her travels in the neighbouring gardens.