Can you ride a scooter? I recommend driving from Chiang Mai to Pai then Mae Hong Son - the ride is so nice through the mountains -- much better than the slow, winding bus!
I had wanted to rent one of the 650cc Kawasakis to do this route but I was the only one who was interested and they are quite expensive!
I lived on Samui for two years and Phang Ngan and Tao are definitely more backpacker orientated. Samui was the place to go 10-20 years back but as the backpackers have blazed the trail, the honeymooners and the families are now more comfortable visiting the place.
Chiang Mai was definitely overrated in my opinion. Overrun with backpackers who are looking for 'the real Thailand'. Furthermore, once you've seen a few temples you've seen them all!
Kanchanaburi is about 3 hours West of BKK by train and is highly recommended POW Railway, Elephant trekking etc (Stay in Ploi Guesthouse!). Ayutthaya looked nice but I only passed through.
If you are going to ship stuff home, make sure you clearly label the box as being a gift as you could get lumped with import tax otherwise.