3 weeks in Thailand, solo trip. Any thoughts?

I just bought my tickets to Thailand for the end of November and would love feedbacks on my itinerary.

My plan is to arrive in Bangkok, flight north to Chiang Rai, go to Chiang Mai, then go to Sukhotai for the loy Krathong (the lights festival). Then Krabi, and finally return back to Bangkok. Sth like:

• Bangkok - 3 full days
• Chiang Rai - 1 full day
• Chiang Mai - 3 full days
• Sukhotai - 2 full days
• Krabi 4 full days

And some extra days travelling between the destinations.

Im not interested in parties or nightlifes, just want a relaxing trip exploring the country. Is this a good plan? 😄