I know you hear a lot of stories about Bessas are great and Bessa are not robust. Everyone has their own standards based on what other equipment they use and what kind of money it's in their wallets. For me, the Bessa R2a was the first rangefinder. Without a direct frame of comparison I thought it was a wonderful camera and I enjoyed every minute of using it. After acquiring an M4, I can see why some people call the Bessa rough.
If you are happy with your Yashica, you'll be quite happy with the Bessa. The Besa might feel lighter, but the nicer VF will make it feel like a better camera in use.