Anasakti Ashram (also called Gandhi Ashram as Mahatma Gandhi had stayed in this Ashram while he was camping at Kasauni) offers simple accommodation.
Call them and make a tentative booking. Post the call, send a letter with self addressed return envelope to
Anashakti Ashram, Kausani,
Mention the dates of travel in the letter. Ashram sends an acknowledgement with reservation booking. Alternately, stay at Hotel Prashant which is right next to Anasakti Ashram or KMVN guesthouse at Kasauni. Hotel Prashant offers decent accommodation at Kasauni. Just walk-in to the hotel, there is no need of advance booking for Hotel Prashant.