I had a look around online to see what kind of programs were available, and KCE stood out as the best option for me. Others were far more expensive, less flexible and involved far larger class sizes.
KCE is great because you can come and stay for as long as you like, and because the classes are all 1-to-1, you can be flexible with the time and topics of your classes. For instance, if you need to take a day off for whatever reason, you can talk to your teacher and reschedule, and they are very understanding and helpful with such requests. I remember doing this on a few occasions so that I could watch the football world cup!