Long-term Japanese course in Tokyo? Small Groups?

Hello everyone :)

I'm contemplating a move to Tokyo for a long-term language course. I'm an entrepreneurial nomad, so I work from my laptop, wherever I am - so finding a job is not an issue. I just really wanted to experience Japan for an extender period of time.

I'm looking for a good, friendly language school in Tokyo, that offers classes for small groups, 5 to 7, not more than 10 people. Does anybody have any experiences doing long term courses in Tokyo? Any ideas of schools that offer less people in a group?

I can only find courses with Protected content and, being almost 30, I don't really fancy an idea of going back to a typical school class ;-) I want something nicer and more immersive.

Thanks in advance for all the tips!