Hi, I'm from Indonesia, and I'm planning to do a backpacking trip from south of thailand all the way up to cambodia around mid december for about a month.
I want to ask, will it be hard if I travel alone? will I be able to find a place to stay or a bus to take if I don't make any reservation before?
Thanks before for your help.
Really easy. I've been backpacking alone in Thailand, Laos and Cambodia for a couple of years (6 separate trips) and have never run into any trouble. However, it may find you if you if you are rude or aggressive (as some westerners can be).
My only advice is:
(1) learn some basic Thai language so you can ask where is a guesthouse or the bus station,
(2) read about Thai cultural norms, and
(3) smile, always smile and have a good heart. It will pay dividends.
Thailand is beautiful and so are Thai people, and I never tire of either.
Low season no problem with hotels or hostels. If it was close to or at Christmas and New Years holidays it would be helpful to have a reservation.
For transportation you shouldn't have a problem in Thailand. You do have to plan ahead though, check the bus and train schedules ahead of time and see when buses depart. This is so you don't show up at a bus or train station and have to wait for hours. I have made reservations a few days prior to using the overnight sleeper train to Chiang Mai. Sleeper trains are pretty popular.
You should have some notion of what you want to see and where to go otherwise you could be wasting your time and money.
Always learn how to say hello and thank you in the language of any country you travel in. You can pick up a cheap English - Thai dictionary and carry it with your. When I have a situation where I don't think my limited Thai is enough to get my point across I take out my little dictionary and point out the exact word I need.
After you get to Thailand you can use a local telephone and call a hotel ahead of time to check on vacancies if you want. Some hotels will reserve a room for you with a phone call.
"....How much will the cost multiply if I go at high season? I'm kinda in tight budget :p."
Expensive hotels really raise the prices up, especially near Christmas and New Years holidays.
Small, cheaper hotels and hostels do increase their prices but not that much. Christmas and New Years may be an exception (they may have parties and buffets) but just for a few days. It's proportional, you won't have a $50 price on a $10 hostel!
If you arrive real late in a town or city you might want to book a room ahead of time just to make sure you have a place to go to. Remember, after you get to Thailand you can also call ahead to make a reservation, often they will hold the room without using a credit card.