Help needed for family adventure.. I've lost my way!

I'm travelling to Thailand next February (4 adults, 2 children aged 7 & 11)

My husband and I travelled through Thailand this year.. North, South & and inbetween & saw some amazing things.

As we will have 2 children with us this time we want to avoid lots of connecting flights & long road journeys.

My plan is to fly to BKK-SUVARNABHUMI, 1 night there, fly to chumphon & spend 5 nights on Ko Tao, on to Koh Phangan (quieter part of the island!) onto Koh Samui & then 3 nights at Khao Sok national park (bamboo rafting, elephant bathing.. No riding!)

Does this seem possible with 3 weeks to do it in?

Any advice greatly appreciated!

I am usually good at planning but it's easier with just 2 of us to plan for. This is a big surprise for my family.. They only know we are in thailand for 3 weeks so I want it to be magical.