One water inlet? No worries. Compact twin showers are perfect for most homes with a wall shower head, where the shower head if fixed directly onto the wall with the arm. A compact twin shower fits onto existing 1/2" plumbing with drill-dree installation, which makes it perfect for retro-fitting!
Having an overhead rain shower, and a hand shower gives you the best of both worlds. Use the overhead for a luxurious full body soak, and the hand held for days when you don't want to wet your hair.