Studying Japanese full-time in Japan?

Hello, I'm living and working in Osaka at the moment. I study Japanese in my spare time, but since I'm an English teacher, I spend so much of my time in an "English bubble".
My level at the moment is between JLPT 3kyu and 2kyu.

I'd like to perhaps dive into the challenge of studying Japanese full-time in Japan, but I don't know much about the available options.

Ideally, I'd like to enrol in a 1 year course at a college, where I would get a student visa (thus allowing me to do some part-time work), and I'd like an intensive course whereby at the end of it I could at least pass 2kyu, or even 1kyu, and in addition to studying for JLPT, I'd like to have lots of very challenging conversation practice to increase my fluency to a high level.

Does anyone have any recommendations on the options available?

Would a university be better than a private language school?

Any advice or comments would be very welcome - I'm only just starting to look into this.

Thanks very much
HP

You might want to look into "Japanese language schools" - those are the places that people who want to attend a university in Japan go to, so that they can get to JLPT level 1. The courses are 1 year, 1.5 years, or 2 years, and with accredited schools your status will be Pre-college visa status, I believe.

Also, just so you know you will not be able to start part time work immediately.
You will need to wait a while (2-3months max) then get permission from the school (who will grant 100%) and immigration