It is true that sourdough loaves (especially ones with crisp crusts) can be difficult to cut into even slices.  I spent ages trying to find a decent bread knife that lasted more than 2 loaves before I had to spend hours sharpening each curve!

I found this one.  I love it and so far the people who have bought it love it too.  And unlike so many serrated knives that are on the market, it's pretty cheap.