I am super jealous of your water.
Low KH soft water.
So yeah, unless you are wanting to keep some hard water fish such as rift lake cichlids a moderate amount of buffering should be fine. You need to raise your KH just a tad to keep things stable.
A natural buffer such as crushed coral should be fine. You do not need a lot of it.
Alternatively you could use chemical additives of which there are numerous. It just depends how you want to the solve the problem. That being said, dropping in some crushed coral is probably easier to manage than using additives. I would probably use chemicals if you wanted more neutral water. Something like Seachem neutral regulator is pretty easy.