Fountain pen. They make some of the best in the world, and if you treat it right it will last your whole life. I've got one that's almost 15 years old. I fill it when it's empty and it's the only pen I use.
From an environmental stand it's great because it's reusable.
From a writing stand it's an amazing feel every time I write.
Sailor, Platinum and Pilot are the big three Japanese brands. You can generally get them outside of Japan but there might be Japan exclusives and the prices might be better in Japan.
Probably enjoying the act of writing, not just getting the job done. I could get through a BIC in about a week if I really tried, but the ink and the feel are pretty horrible.
From an environmental stand it's great because it's reusable.
From a writing stand it's an amazing feel every time I write.