Which JR Pass Should I Buy For My Trip To Japan?

Hi!

This November-December me and my boyfriend will be going to Japan together.
I'm struggling a bit to decide on buying a JR pass or buying tickets individually for transportation we need to catch.
If it is a JR pass, which one?

If someone could help me decide from our planned trip below, that would be great! :)

Tokyo to Fujikawaguchiko - 28th of Nov (staying in Fujikawaguchiko till the 1st of Dec)

Fujikawaguchiko to Nagoya - 1st of Dec (staying in Nagoya till the 4th of Dec)

Nagoya to Shiga - 4th of Dec (staying in Shiga till the 7th of Dec)

Shiga to Osaka - 7th of Dec (staying in Osaka till the 11th of Dec)

Osaka to Nagano - 11th of Dec (staying in Nagano until 13th of Dec)

Nagano to Tokyo - 13th of Dec (staying in Tokyo until the 16th of Dec)

Total stay: 20 days.

I am aware for Fujikawaguchiko we would most likely take a bus but for the rest, I'm not so sure.
Any help would be super appreciated!

Thank you!