Booking hostels are probably the most affordable and convenient way to travel. Unlike hotels, hostels may involve sharing dorms with others which is what makes it a lot cheaper but more fun as you make new friends. Most hostels are also located near to transport links. And yes - for added peace of mind your best bet is to book your hostel in advance for the first part of your trip. After that, the great thing about hostelling is that you can go with the flow and easily check in to a room/dorm as your journey continues.