I have been living and/or traveling to Thailand for almost 30 years. Over that time, my wife (Thai) and I have stayed at a lot of places. This has to be one of our favorites. The owners are friendly and helpful. The resort and small open air restaurant are extremely well kept. There is an attention to detail that you don't often see, regardless of country.
Keep in mind that this resort is a true small business, not a corporate run hotel out of Bangkok. There is a small, friendly staff of employees who do everything from cook and serve the food and drinks; keep the grounds and pool tidy; tend to their small herb and vegetable garden, and clean the cottages. Occasionally, you might have to wait a few extra minutes for a cup of coffee or your food than you would at a big corporate hotel chain. But that is a tiny price to pay for being able to stay at a such unique and charming place. The owners/managers are fluent in English, Dutch, Thai, and perhaps other languages as well.
The next time my wife I visit Mae Rim again, we are certain where we will be staying--Monoceros.