My first project had a genitive particle /je/ that went between the possessor and possessed. In one of my more recent projects, I used a Nahuatl form of possession, so “the fish’s flower” would be “its-flower fish”, and “my coffee” would be “my-coffee I”. There was a possessive prefix for each pronoun, but over time via evolution the pronoun system got much more complicated, but the prefixes stayed the same, leading to an interesting result.

I think a cool system would be the Nahuatl system but the affixes are infixes because it is as if the possessor is surrounding what he owns. Also, having more than one way to express a concept in a language can make it more interesting, so why not do that with possession? Just some ideas.