Oops, sorry. I totally forgot about Schnorr.
However we should be able go get Schnorr Signatures, that's just a soft fork isn't it..?
Yup. Segwit's version script system allows for Schnorr signature to be activated without a hard fork.
It's not totally clear to me from your answer above..Can you please confirm that we can achieve coin-join transactions that are cheaper than normal transactions with the use of Schnorr Signatures only?
Likely not. Schnorr signature can combine the signatures of the non segwit transactions into one. While this could be useful if you're using CoinJoin to spend several inputs, I would expect the price to be the same whether you're spending it with or without using CoinJoin.
So we actually don't need Bulletproofs for this to happen?
No.