Thanks a million for all of your replies. We will probably just take it in our stride now or maybe do two. We are looking for relaxation, activities and some partying, so based on that which would be better koh phangan or kao Tao. Also, would it be too much of a trek back from Kao Tao to Surat airport on the same day as our flight which is at 3pm.
Also, could you recommend an area/accommodation in each of the islands especially Koh Samui that would be good to stay in.

It is wet season on the West coast in August. Don't book places in advance (1) you won't need to (2) you should stay flexible. If the weather is too bad, you can head over to the East side (Koh Tao, Ko Phangnan, Ko Samui) where it should be better.

Phi Phi's South East and East coast are fairly quiet, but check how rough the seas are before taking a boat there . with children.

Thanks a lot for all the recommendations!

Yes, 5+5+5 Euro covers the basic of the basics for you.

Awesome, then that might actually work!

Koh Phangan and Koh Tao (and Samui) are better during that time of the year weather wise, less affected by the South West monsoon, so might be better for the beach part.

Just did some research on the monsoon part and that seems to be quite an issue in the Andaman Sea, right?
In terms of the weather, it is currently pretty much raining all the time, is that likely going to be the same in August like now?

Sukhothai might be a good stop in the north, see temples by bicycle, has hostels, then up to Chiang Mai. Pai is another favourite stop in the North.

Combine that with the islands in the South and Bangkok and you're busy for a month.

Could stop in Prachuap Kiri Khan, should be possible to find something around 250-300 baht there, low key seaside town, bicycle to local beaches, can break up the journey to the South.

That looks really nice. Didn't think about biking before but actually seems like a very nice idea.
Is there anything I should know about hiring and riding bikes in Thailand?
I'm also going to search on the forum for tips on that.

Use 2nd class and 3rd class seats in trains, very cheap, and fine for those trips (if you do long distance Bkk-Chiang Mai non-stop better take overnight sleeper, cost more, but more comfy for the longer ride, plus safe overnight accommodation).

Yes planned on doing that anyway but with the sleeper might be an option too then.

Might have to buy a bottle of Sang Som or Mekong and mix with coke instead of drinking beer.

Sounds good, gonna try that!

If you want to travel slow and cheaply, or perhaps a better wird is frugally, it's still possible.. I often say to others I will meet you there, and then travel in my style.. Why shouldn't I take a 10 rupee bus and meet some locals instead of the 300 rupee taxi where I save about 8 minutes.. I have the time!! But I also choose more expensive options when the time is right....

There are plenty of old fashioned travelers who know what travel means to them,And still travel that way, although booking. Com does have its occasional attraction..

Fear not...!! If you ever go back to Samui, there are sides to the island that you would think time stood still and if you know a bit of Thai, some very inexpensive places in the 175£ a month range with AC, hot water, and a fridge.. Just in case....

You should get to Ankor sooner then later!!! Out of season!!

Two and a half weeks?
As a framework I would pick a couple of destinations plus Bangkok.
Most people fly into Bkk, but wherever you land it is a good idea to have a night or two pre-booked. After that you could book as you go depending on how the mood takes you and where you go. High season mid November to January may need a bit more booking.
Most people want a spell on Thailand's beaches and then a bit of "culture" or nature in the north.
For beaches you have the Andaman coast, e g. Krabi, Phuket or the East coast gulf islands of Samui or Koh Chang.
Flying is the easiest and most convenient way of travel, but coaches and trains are cheap.
For culture and nature I'd recommend either Kanchanaburi in the West or Chiang Mai in the north.
At the end of you stay you might want to spend another night or two in Bkk before flying out.
Hotels should be happy to help you ring ahead to your next destination and help you book rooms or you might want to pre-book an itinerary. The problem with this is it leaves little flexibility in your schedule.
Thailand is a relatively "soft" option for tourists these days and is very much geared up for tourism. The tourist lingua franca is English and spoken to varying degrees pretty much everywhere.
You will also find Chinese and Russian especially in the more urban hotspots

Just to warn the main beaches of Ko Samui such as Lamai and Chaweng are fairly built up and a bit expensive and it can be a an insular experience being on resort beaches among random mainstream tourists . Some still enjoy these beaches but others don't . If you are on a budget you might be better off on Ko Phangan which although is turning into another Ko Samui does have cheaper accomm on some of the beaches.

URL: https://www.instagram.com/p/BbEpT1ngt1x/?taken-by=nomadic_chica

Destination: Maeklong Railway Market, Samut Songkhram, Thailand.

Context: Maeklong Railway Market is considered to be the most dangerous market in the world.
It runs through the train lines where the train actually passes twice a day!!
I had this on my pending list since last time I was in Thailand and I couldn't manage to get there when the train was passing. This time I've done all the research and I could finally be there when the train was arriving at Maeklong, it's very exciting to be standing so close to the train, with the vendors hyper-relaxed while they move some of their products to allow the train go to the station.
A fun experience and amazing for markets freaks like me!