Achemilla mollis (Our Lady's Mantle) is dead easy to grow - once you've got it! By that I mean that a mature plant will self sow promiscuously all over your garden - also it is easy to divide.. The trick is getting a plant in the first place. I have never sown seeds, but bought one small plant 20 years ago.
My mother is absolutely unable to grow this plant from seed, which I have given her several times from my own plants. Yet I have a beautiful mature plant growing in gravel which self seeded from one in a pot which I brought with me when I moved here. And the one in the pot was a self sown from my old garden!
So, if you do sow from seed - just sow a very few plants say 3 - 6 and pass on your leftovers. Because once you have successfully grown a Lady's Mantle, this wonderful plant will be with you forever!
Alternatively, why not buy a small plant from the garden centre, 1 plant = several next year. Oh and once the plant has flowered do remember to cut it right down if you DON'T want seedlings everywhere. Hope all is clear, good luck. Regards Caro