My husband and I (late 30s Canadians) stayed here for 9 nights on vacation around new year and we had an absolutely amazing time. Casa de la Ballena is like a perfect little oasis in the middle of a bustling town full of construction, and is only a 5 minute walk to the town centre or the beach.
We were in room #1, and it was clean and spacious, with a king size bed, kitchenette and large refrigerator, AC, a safe, nice space to hang clothing, and a TV.
The common space is quiet and relaxing and there is soft music playing all day, Our stay included breakfast every morning, fresh fruit and yogurt and coffee as well as cooked to order hot dishes. The staff was wonderful and the host, Martin, was simply lovely (and his english was excellent).
An amazing feature they offer is that they have a filtration system for the water in the entire facility, so you can drink safely from the taps and avoid constantly buying bottles (basically unheard of around there).
I highly recommend this spot for a safe, secure, relaxing stay while you're in Sayulita!