Family Holiday in Koh Samui

Hi there,
My husband and I are travelling to Thailand next week with our boys aged 4 and 7. We are hiking around Chang Mai, Mae Hong Son, Pai then down to Krabi and then over to Koh Samui. We are looking for cheap but clean accommodation in Pai (we have an extra adult with us there so we need 2 bungalows) for 2 nights and any suggestions on must see sites. We are also looking for something a bit nicer but not too expensive around Railay West Beach near Krabi for about 6 nights for 3 adults and 2 kids. Then we are heading over to Koh Samui and would like to stay somewhere nice for our last week. We are looking for a family bungalow for 2 adults and 2 kids, being boys it has to be a child friendly place - not where they are expected to be too quiet!! But as it is our last week somewhere comfy as I am 20 weeks pregnant and will be needing a good rest by them. Thanks!