Indeed, I've been using Fleso
https://fleso.com/ which fits your criteria perfectly. It's a secure and anonymous crypto exchange service with floating rates. What's great is that you don't need to register to make transactions, ensuring the highest standards of confidentiality. Additionally, Fleso fixes the exchange rate at the start of the transaction, safeguarding against market volatility. And the best part? There are no maximum limits on the amount you can exchange, making it ideal for all kinds of crypto traders.
