The word 'boni' sounds pretty weird and isn't recognized by spelling correctors, but following normal english grammar it should exist.

Bonsi would be a really nice plural form of bonus.

Boni sounds Latin. Admittedly, lots of English words come from either Latin or French. But I'm fairly sure we use the word 'bonuses'.

Bonuses in english, Boni in latin.

The word is originally latin but has been anglicized.

Boni is the plural form of the latin word "bonus". (Or it is the genitive singular, but never mind about that one).
The word usually means "good", although it has multiple other similar meanings.

I believe the english word bonus does come from the latin version. But all sources say that the correct english form is "bonuses". So, if you are writing in English, you should write down bonuses and not boni.