Suggestions for improving my 2 week Thailand itinerary

I am visiting Thailand with my friends for 2 weeks starting from mid-December this year.

Had prepared a rough itinerary, need help with 2 things please

  1. Suggestions for improving it, if I should replace some place with other or any sites which I must visit within the places mentioned or any must-do activities.
  2. Recommendation of stay at each location would be really helpful considering it being near to tourist places, or either is a really good place to stay in terms of view or vibe (preferred hostel, can do an Airbnb if it's too awesome)

We wanna be at a lively and happening place but also wanna be at a relaxing place in between, a good balance. Looking for a budget trip and collecting different experiences.

Itinerary:

Day 1-2: Bangkok

Day 3-4: Khao Sok (stay book here: https://khaosoklake.com/), how to reach here?

Day 5,6,7,8: Phuket + Krabi (water sports, activities and boat tours nearby)

Day 9,10: Phi phi (tour to Maya bay)

Day 11,12,13: Koh lipe

Day 14: travel mostly to reach Bangkok

Day 15: catch flight home

I had not included the Gulf coast islands cause its rainy season around this time there.

Another question:

- Will I have to buy 20kg checked-in luggage for Thailand domestic flights also? Any airline which has this included? Will prefer that for internal transfers like Bangkok to Suraj Thani, Hat yai to Bangkok etc