Fear not, we've got you (and your mattress!) covered. We have solved this problem by adding elastic all the way around the bottom of all our fitted sheets to keep them snug on your mattress all night long. Make sure you have the correct size and depth (36 or 40cm available here), make sure it's the correct way round on your mattress and give it a good tuck in and you should be set for a very restful night indeed.