Yes, the Altug Meis Lines boat leaves Kas at around 10am every weekday. Aim to be there by 9.30 so that passport formalities can be completed. Their new ferry carries 140 passengers and there's less need now to book in advance.
There is a small beach on Meis. As you enter the harbour there's a pathway on the left that goes around the island past the old mosque. There are a couple of places around there a that are good for bathing. But If you carry on another 100 metres or so there's another smaller harbour which has a small beach and pontoons to swim out to.