When I think of a boutique hotel SIXTY Soho comes to mind. It is sophisticated, modern, serene, hip with a mix of locals and international clientele. There is a small gym on site. If you choose, access is given to a commercial gym nearby. The bar is chic and the onsite restaurant is very tasty.
The staff is extremely accommodating and make you feel like family. The Soho location is perfect for shopping and restaurants.