All gorgeous beaches, some with more rock pools than others, but all very beautiful and definitely solo friendly.
Hello Hannah and welcome to the solo forum. If you can travel between July and mid September, I’d suggest the Brittany coast of northern France, pretty much all of the Cornwall coast in the UK, the west coast of Portugal and the west coast of Ireland, particularly in Dingle. All gorgeous beaches, some with more rock pools than others, but all very beautiful and definitely solo friendly. The waters are warmer towards the end of August onwards and the usual summer crowds thin out after August.