After I tried different travel agencies which were focused on backpackers there seems to be another Tour Operator with focuses more on high end tourism. They are pretty successfull in Ecuador with Galapagos and started to offer tours here in Bolivia as well. www.surtrek.bo
I went with them on the uyuni salar and the lagoons, they seem very good organized. To be honest, I rather spend some dollars more in a good trip instead of having a driver who is not willing to bring me where I want to go (isla del sol etc.)