8 days in Thailand Itinerary help

Hello everyone,

I will be in Thailand for 8 days. I need help with making my itinerary excluding bangkok. I am confused between doing Koh Samui, Phuket and Krabi Or Just Krabi and Phuket. Do you think doing all 3 would be too tight?

I am worried about reaching Koh Samui from Bangkok and from Samui to Phuket/Krabi.