Slashing a loaf of very loose bread dough can be quite an experience. I've found a way that works on even very soft dough, without deforming or tearing the loaf. This sounds rediculous, but it works.
An electric knife will cut the most slack dough without deforming the loaf. It takes practice, don't press down or you'll cut your loaf to the bottom. The knife blade doesn't even get dirty. No dough sticks to it and if you don't have one, you should be able to get a low cost knife for $5.00 at a Big Lots or other discount store. Give it a try.